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 $58.71   7.460%   $63.0898   $63.09   $63.10   $63.10  
  Purchase #2 $244.57   5.158%   $257.1849   $257.18   $257.20   $257.20  
  Purchase #3 $100.83   4.359%   $105.2252   $105.23   $105.25   $105.20  
  Purchase #4 $176.26   8.555%   $191.339   $191.34   $191.35   $191.30  
  Purchase #5 $206.48   7.793%   $222.571   $222.57   $222.55   $222.60  
  Purchase #6 $28.66   4.560%   $29.9669   $29.97   $29.95   $30.00  
  Purchase #7 $148.67   13.846%   $169.2548   $169.25   $169.25   $169.30  
  7 purchase totals = $964.18       $1,038.6316   $1,038.63   $1,038.65   $1,038.70