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 $48.94   3.206%   $50.509   $50.51   $50.50   $50.50  
  Purchase #2 $226.42   10.259%   $249.6484   $249.65   $249.65   $249.60  
  Purchase #3 $18.79   8.494%   $20.386   $20.39   $20.40   $20.40  
  Purchase #4 $130.29   4.269%   $135.8521   $135.85   $135.85   $135.90  
  Purchase #5 $206.37   6.431%   $219.6417   $219.64   $219.65   $219.60  
  Purchase #6 $174.83   11.403%   $194.7659   $194.77   $194.75   $194.80  
  Purchase #7 $138.56   11.778%   $154.8796   $154.88   $154.90   $154.90  
  7 purchase totals = $944.20       $1,025.6827   $1,025.69   $1,025.70   $1,025.70