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 $54.61   7.355%   $58.6266   $58.63   $58.65   $58.60  
  Purchase #2 $199.44   5.455%   $210.3195   $210.32   $210.30   $210.30  
  Purchase #3 $63.49   8.658%   $68.987   $68.99   $69.00   $69.00  
  Purchase #4 $121.36   9.198%   $132.5227   $132.52   $132.50   $132.50  
  Purchase #5 $153.66   8.273%   $166.3723   $166.37   $166.35   $166.40  
  Purchase #6 $60.86   12.743%   $68.6154   $68.62   $68.60   $68.60  
  Purchase #7 $62.38   11.674%   $69.6622   $69.66   $69.65   $69.70  
  7 purchase totals = $715.80       $775.1057   $775.11   $775.05   $775.10