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 $216.66   9.377%   $236.9762   $236.98   $237.00   $237.00  
  Purchase #2 $37.92   8.416%   $41.1113   $41.11   $41.10   $41.10  
  Purchase #3 $244.26   11.302%   $271.8663   $271.87   $271.85   $271.90  
  Purchase #4 $50.47   10.116%   $55.5755   $55.58   $55.60   $55.60  
  Purchase #5 $149.48   8.358%   $161.9735   $161.97   $161.95   $162.00  
  Purchase #6 $151.48   8.859%   $164.8996   $164.90   $164.90   $164.90  
  Purchase #7 $45.61   6.456%   $48.5546   $48.55   $48.55   $48.60  
  7 purchase totals = $895.88       $980.9570   $980.96   $980.95   $981.10