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 $52.54   10.229%   $57.9143   $57.91   $57.90   $57.90  
  Purchase #2 $206.41   9.487%   $225.9921   $225.99   $226.00   $226.00  
  Purchase #3 $101.75   8.156%   $110.0487   $110.05   $110.05   $110.00  
  Purchase #4 $22.32   11.321%   $24.8468   $24.85   $24.85   $24.80  
  Purchase #5 $14.81   3.739%   $15.3637   $15.36   $15.35   $15.40  
  Purchase #6 $220.98   11.312%   $245.9773   $245.98   $246.00   $246.00  
  Purchase #7 $237.50   10.812%   $263.1785   $263.18   $263.20   $263.20  
  7 purchase totals = $856.31       $943.3214   $943.32   $943.35   $943.30