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 $132.57   6.713%   $141.4694   $141.47   $141.45   $141.50  
  Purchase #2 $227.30   6.182%   $241.3517   $241.35   $241.35   $241.40  
  Purchase #3 $143.89   4.140%   $149.847   $149.85   $149.85   $149.80  
  Purchase #4 $250.53   10.343%   $276.4423   $276.44   $276.45   $276.40  
  Purchase #5 $243.99   11.738%   $272.6295   $272.63   $272.65   $272.60  
  Purchase #6 $64.93   13.541%   $73.7222   $73.72   $73.70   $73.70  
  Purchase #7 $249.65   4.166%   $260.0504   $260.05   $260.05   $260.10  
  7 purchase totals = $1,312.86       $1,415.5125   $1,415.51   $1,415.50   $1,415.50