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 $108.88   8.311%   $117.929   $117.93   $117.95   $117.90  
  Purchase #2 $118.47   5.443%   $124.9183   $124.92   $124.90   $124.90  
  Purchase #3 $62.49   11.402%   $69.6151   $69.62   $69.60   $69.60  
  Purchase #4 $67.44   8.270%   $73.0173   $73.02   $73.00   $73.00  
  Purchase #5 $168.97   8.163%   $182.763   $182.76   $182.75   $182.80  
  Purchase #6 $229.45   6.769%   $244.9815   $244.98   $245.00   $245.00  
  Purchase #7 $127.55   10.202%   $140.5627   $140.56   $140.55   $140.60  
  7 purchase totals = $883.25       $953.7869   $953.79   $953.75   $953.80