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 $60.88   8.279%   $65.9203   $65.92   $65.90   $65.90  
  Purchase #2 $125.87   13.573%   $142.9543   $142.95   $142.95   $143.00  
  Purchase #3 $222.26   3.239%   $229.459   $229.46   $229.45   $229.50  
  Purchase #4 $130.85   9.409%   $143.1617   $143.16   $143.15   $143.20  
  Purchase #5 $204.85   10.360%   $226.0725   $226.07   $226.05   $226.10  
  Purchase #6 $124.26   10.304%   $137.0638   $137.06   $137.05   $137.10  
  Purchase #7 $241.58   9.233%   $263.8851   $263.89   $263.90   $263.90  
  7 purchase totals = $1,110.55       $1,208.5167   $1,208.51   $1,208.45   $1,208.70