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 $124.80   13.354%   $141.4658   $141.47   $141.45   $141.50  
  Purchase #2 $222.85   9.761%   $244.6024   $244.60   $244.60   $244.60  
  Purchase #3 $166.93   12.394%   $187.6193   $187.62   $187.60   $187.60  
  Purchase #4 $100.99   11.225%   $112.3261   $112.33   $112.35   $112.30  
  Purchase #5 $247.29   11.511%   $275.7556   $275.76   $275.75   $275.80  
  Purchase #6 $181.73   3.105%   $187.3727   $187.37   $187.35   $187.40  
  Purchase #7 $201.96   7.769%   $217.6503   $217.65   $217.65   $217.70  
  7 purchase totals = $1,246.55       $1,366.7922   $1,366.80   $1,366.75   $1,366.90