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 $91.91   12.347%   $103.2581   $103.26   $103.25   $103.30  
  Purchase #2 $54.39   9.603%   $59.6131   $59.61   $59.60   $59.60  
  Purchase #3 $34.84   13.539%   $39.557   $39.56   $39.55   $39.60  
  Purchase #4 $50.84   12.139%   $57.0115   $57.01   $57.00   $57.00  
  Purchase #5 $193.48   8.814%   $210.5333   $210.53   $210.55   $210.50  
  Purchase #6 $102.93   3.407%   $106.4368   $106.44   $106.45   $106.40  
  Purchase #7 $123.91   13.781%   $140.986   $140.99   $141.00   $141.00  
  7 purchase totals = $652.30       $717.3958   $717.40   $717.40   $717.40