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 $55.66   11.207%   $61.8978   $61.90   $61.90   $61.90  
  Purchase #2 $168.92   5.748%   $178.6295   $178.63   $178.65   $178.60  
  Purchase #3 $180.77   4.573%   $189.0366   $189.04   $189.05   $189.00  
  Purchase #4 $52.71   8.103%   $56.9811   $56.98   $57.00   $57.00  
  Purchase #5 $28.56   12.502%   $32.1306   $32.13   $32.15   $32.10  
  Purchase #6 $136.71   9.416%   $149.5826   $149.58   $149.60   $149.60  
  Purchase #7 $72.36   5.608%   $76.4179   $76.42   $76.40   $76.40  
  7 purchase totals = $695.69       $744.6761   $744.68   $744.75   $744.60