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 $234.37   13.665%   $266.3967   $266.40   $266.40   $266.40  
  Purchase #2 $45.70   5.646%   $48.2802   $48.28   $48.30   $48.30  
  Purchase #3 $67.27   8.229%   $72.8056   $72.81   $72.80   $72.80  
  Purchase #4 $202.93   9.387%   $221.979   $221.98   $222.00   $222.00  
  Purchase #5 $171.97   13.871%   $195.824   $195.82   $195.80   $195.80  
  Purchase #6 $97.51   8.272%   $105.576   $105.58   $105.60   $105.60  
  Purchase #7 $71.39   4.459%   $74.5733   $74.57   $74.55   $74.60  
  7 purchase totals = $891.14       $985.4348   $985.44   $985.45   $985.50