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 $96.72   11.364%   $107.7113   $107.71   $107.70   $107.70  
  Purchase #2 $197.49   7.467%   $212.2366   $212.24   $212.25   $212.20  
  Purchase #3 $99.52   5.511%   $105.0045   $105.00   $105.00   $105.00  
  Purchase #4 $71.98   5.759%   $76.1253   $76.13   $76.15   $76.10  
  Purchase #5 $150.34   3.322%   $155.3343   $155.33   $155.35   $155.30  
  Purchase #6 $61.49   11.765%   $68.7243   $68.72   $68.70   $68.70  
  Purchase #7 $78.48   8.237%   $84.9444   $84.94   $84.95   $84.90  
  7 purchase totals = $756.02       $810.0807   $810.07   $810.10   $809.90