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 $164.54   8.159%   $177.9648   $177.96   $177.95   $178.00  
  Purchase #2 $38.66   13.433%   $43.8532   $43.85   $43.85   $43.90  
  Purchase #3 $91.94   11.555%   $102.5637   $102.56   $102.55   $102.60  
  Purchase #4 $155.40   6.292%   $165.1778   $165.18   $165.20   $165.20  
  Purchase #5 $201.79   4.799%   $211.4739   $211.47   $211.45   $211.50  
  Purchase #6 $161.54   11.815%   $180.626   $180.63   $180.65   $180.60  
  Purchase #7 $69.55   8.173%   $75.2343   $75.23   $75.25   $75.20  
  7 purchase totals = $883.42       $956.8937   $956.88   $956.90   $957.00