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 $191.38   13.871%   $217.9263   $217.93   $217.95   $217.90  
  Purchase #2 $236.97   10.120%   $260.9514   $260.95   $260.95   $261.00  
  Purchase #3 $139.99   9.470%   $153.2471   $153.25   $153.25   $153.20  
  Purchase #4 $171.56   8.590%   $186.297   $186.30   $186.30   $186.30  
  Purchase #5 $25.76   8.522%   $27.9553   $27.96   $27.95   $28.00  
  Purchase #6 $61.57   4.299%   $64.2169   $64.22   $64.20   $64.20  
  Purchase #7 $183.96   9.813%   $202.012   $202.01   $202.00   $202.00  
  7 purchase totals = $1,011.19       $1,112.6060   $1,112.62   $1,112.60   $1,112.60