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 $111.48   13.413%   $126.4328   $126.43   $126.45   $126.40  
  Purchase #2 $212.68   6.870%   $227.2911   $227.29   $227.30   $227.30  
  Purchase #3 $144.28   10.453%   $159.3616   $159.36   $159.35   $159.40  
  Purchase #4 $117.31   12.617%   $132.111   $132.11   $132.10   $132.10  
  Purchase #5 $161.46   13.262%   $182.8728   $182.87   $182.85   $182.90  
  Purchase #6 $5.62   8.470%   $6.096   $6.10   $6.10   $6.10  
  Purchase #7 $118.31   7.505%   $127.1892   $127.19   $127.20   $127.20  
  7 purchase totals = $871.14       $961.3545   $961.35   $961.35   $961.40