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 $161.56   4.654%   $169.079   $169.08   $169.10   $169.10  
  Purchase #2 $104.95   7.552%   $112.8758   $112.88   $112.90   $112.90  
  Purchase #3 $32.54   8.297%   $35.2398   $35.24   $35.25   $35.20  
  Purchase #4 $199.96   11.633%   $223.2213   $223.22   $223.20   $223.20  
  Purchase #5 $89.43   9.622%   $98.035   $98.04   $98.05   $98.00  
  Purchase #6 $228.95   5.171%   $240.789   $240.79   $240.80   $240.80  
  Purchase #7 $43.25   9.192%   $47.2255   $47.23   $47.25   $47.20  
  7 purchase totals = $860.64       $926.4654   $926.48   $926.55   $926.40