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 $89.66   5.206%   $94.3277   $94.33   $94.35   $94.30  
  Purchase #2 $224.54   4.846%   $235.4212   $235.42   $235.40   $235.40  
  Purchase #3 $19.51   12.190%   $21.8883   $21.89   $21.90   $21.90  
  Purchase #4 $149.50   5.560%   $157.8122   $157.81   $157.80   $157.80  
  Purchase #5 $193.68   3.755%   $200.9527   $200.95   $200.95   $201.00  
  Purchase #6 $166.81   13.553%   $189.4178   $189.42   $189.40   $189.40  
  Purchase #7 $115.54   8.470%   $125.3262   $125.33   $125.35   $125.30  
  7 purchase totals = $959.24       $1,025.1461   $1,025.15   $1,025.15   $1,025.10