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 $30.74   8.184%   $33.2558   $33.26   $33.25   $33.30  
  Purchase #2 $197.98   3.177%   $204.2698   $204.27   $204.25   $204.30  
  Purchase #3 $119.72   4.291%   $124.8572   $124.86   $124.85   $124.90  
  Purchase #4 $21.65   12.377%   $24.3296   $24.33   $24.35   $24.30  
  Purchase #5 $196.81   4.786%   $206.2293   $206.23   $206.25   $206.20  
  Purchase #6 $202.39   3.242%   $208.9515   $208.95   $208.95   $209.00  
  Purchase #7 $229.47   3.128%   $236.6478   $236.65   $236.65   $236.60  
  7 purchase totals = $998.76       $1,038.5410   $1,038.55   $1,038.55   $1,038.60