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 $53.98   9.517%   $59.1173   $59.12   $59.10   $59.10  
  Purchase #2 $173.34   4.253%   $180.7122   $180.71   $180.70   $180.70  
  Purchase #3 $143.71   4.639%   $150.3767   $150.38   $150.40   $150.40  
  Purchase #4 $158.96   4.384%   $165.9288   $165.93   $165.95   $165.90  
  Purchase #5 $248.51   9.671%   $272.5434   $272.54   $272.55   $272.50  
  Purchase #6 $62.67   11.396%   $69.8119   $69.81   $69.80   $69.80  
  Purchase #7 $117.64   6.546%   $125.3407   $125.34   $125.35   $125.30  
  7 purchase totals = $958.81       $1,023.8310   $1,023.83   $1,023.85   $1,023.70