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 $52.51   3.647%   $54.425   $54.43   $54.45   $54.40  
  Purchase #2 $249.68   4.310%   $260.4412   $260.44   $260.45   $260.40  
  Purchase #3 $25.70   11.708%   $28.709   $28.71   $28.70   $28.70  
  Purchase #4 $211.65   10.102%   $233.0309   $233.03   $233.05   $233.00  
  Purchase #5 $67.47   8.801%   $73.408   $73.41   $73.40   $73.40  
  Purchase #6 $90.89   3.446%   $94.0221   $94.02   $94.00   $94.00  
  Purchase #7 $90.37   8.131%   $97.718   $97.72   $97.70   $97.70  
  7 purchase totals = $788.27       $841.7542   $841.76   $841.75   $841.60