Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.97   13.532%   $267.9015   $267.90   $267.90   $267.90  
  Purchase #2 $188.73   10.838%   $209.1846   $209.18   $209.20   $209.20  
  Purchase #3 $165.63   12.597%   $186.4944   $186.49   $186.50   $186.50  
  Purchase #4 $53.86   13.406%   $61.0805   $61.08   $61.10   $61.10  
  Purchase #5 $156.42   11.188%   $173.9203   $173.92   $173.90   $173.90  
  Purchase #6 $215.57   12.295%   $242.0743   $242.07   $242.05   $242.10  
  Purchase #7 $190.32   8.106%   $205.7473   $205.75   $205.75   $205.70  
  7 purchase totals = $1,206.50       $1,346.4029   $1,346.39   $1,346.40   $1,346.40