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 $87.63   9.736%   $96.1617   $96.16   $96.15   $96.20  
  Purchase #2 $119.96   12.536%   $134.9982   $135.00   $135.00   $135.00  
  Purchase #3 $48.96   5.760%   $51.7801   $51.78   $51.80   $51.80  
  Purchase #4 $200.78   6.815%   $214.4632   $214.46   $214.45   $214.50  
  Purchase #5 $55.85   13.415%   $63.3423   $63.34   $63.35   $63.30  
  Purchase #6 $88.93   11.534%   $99.1872   $99.19   $99.20   $99.20  
  Purchase #7 $12.40   5.783%   $13.1171   $13.12   $13.10   $13.10  
  7 purchase totals = $614.51       $673.0498   $673.05   $673.05   $673.10