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 $108.47   13.494%   $123.1069   $123.11   $123.10   $123.10  
  Purchase #2 $170.82   13.505%   $193.8892   $193.89   $193.90   $193.90  
  Purchase #3 $51.89   13.469%   $58.8791   $58.88   $58.90   $58.90  
  Purchase #4 $217.45   13.465%   $246.7296   $246.73   $246.75   $246.70  
  Purchase #5 $207.46   5.359%   $218.5778   $218.58   $218.60   $218.60  
  Purchase #6 $116.97   4.683%   $122.4477   $122.45   $122.45   $122.40  
  Purchase #7 $66.88   7.646%   $71.9936   $71.99   $72.00   $72.00  
  7 purchase totals = $939.94       $1,035.6239   $1,035.63   $1,035.70   $1,035.60