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 $111.82   6.263%   $118.8233   $118.82   $118.80   $118.80  
  Purchase #2 $57.75   13.761%   $65.697   $65.70   $65.70   $65.70  
  Purchase #3 $126.61   13.775%   $144.0505   $144.05   $144.05   $144.10  
  Purchase #4 $176.91   12.342%   $198.7442   $198.74   $198.75   $198.70  
  Purchase #5 $21.95   8.397%   $23.7931   $23.79   $23.80   $23.80  
  Purchase #6 $57.76   3.738%   $59.9191   $59.92   $59.90   $59.90  
  Purchase #7 $99.65   12.389%   $111.9956   $112.00   $112.00   $112.00  
  7 purchase totals = $652.45       $723.0228   $723.02   $723.00   $723.00