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 $125.32   5.860%   $132.6638   $132.66   $132.65   $132.70  
  Purchase #2 $59.27   11.366%   $66.0066   $66.01   $66.00   $66.00  
  Purchase #3 $160.55   6.110%   $170.3596   $170.36   $170.35   $170.40  
  Purchase #4 $26.83   9.114%   $29.2753   $29.28   $29.30   $29.30  
  Purchase #5 $178.78   13.727%   $203.3211   $203.32   $203.30   $203.30  
  Purchase #6 $247.60   10.445%   $273.4618   $273.46   $273.45   $273.50  
  Purchase #7 $69.36   5.566%   $73.2206   $73.22   $73.20   $73.20  
  7 purchase totals = $867.71       $948.3088   $948.31   $948.25   $948.40