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 $63.32   4.250%   $66.0111   $66.01   $66.00   $66.00  
  Purchase #2 $155.75   4.844%   $163.2945   $163.29   $163.30   $163.30  
  Purchase #3 $139.49   10.564%   $154.2257   $154.23   $154.25   $154.20  
  Purchase #4 $64.52   13.631%   $73.3147   $73.31   $73.30   $73.30  
  Purchase #5 $236.65   4.633%   $247.614   $247.61   $247.60   $247.60  
  Purchase #6 $93.57   8.694%   $101.705   $101.71   $101.70   $101.70  
  Purchase #7 $99.49   12.639%   $112.0645   $112.06   $112.05   $112.10  
  7 purchase totals = $852.79       $918.2295   $918.22   $918.20   $918.20