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 $118.78   13.620%   $134.9578   $134.96   $134.95   $135.00  
  Purchase #2 $192.65   11.534%   $214.8703   $214.87   $214.85   $214.90  
  Purchase #3 $47.31   8.443%   $51.3044   $51.30   $51.30   $51.30  
  Purchase #4 $104.48   5.354%   $110.0739   $110.07   $110.05   $110.10  
  Purchase #5 $179.62   4.766%   $188.1807   $188.18   $188.20   $188.20  
  Purchase #6 $155.53   9.413%   $170.17   $170.17   $170.15   $170.20  
  Purchase #7 $231.60   8.302%   $250.8274   $250.83   $250.85   $250.80  
  7 purchase totals = $1,029.97       $1,120.3845   $1,120.38   $1,120.35   $1,120.50