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 $32.68   7.461%   $35.1183   $35.12   $35.10   $35.10  
  Purchase #2 $199.54   12.758%   $224.9973   $225.00   $225.00   $225.00  
  Purchase #3 $28.46   13.189%   $32.2136   $32.21   $32.20   $32.20  
  Purchase #4 $94.70   9.843%   $104.0213   $104.02   $104.00   $104.00  
  Purchase #5 $244.70   5.331%   $257.745   $257.75   $257.75   $257.70  
  Purchase #6 $139.29   12.428%   $156.601   $156.60   $156.60   $156.60  
  Purchase #7 $195.39   13.363%   $221.5   $221.50   $221.50   $221.50  
  7 purchase totals = $934.76       $1,032.1965   $1,032.20   $1,032.15   $1,032.10