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 $133.61   9.279%   $146.0077   $146.01   $146.00   $146.00  
  Purchase #2 $195.26   11.819%   $218.3378   $218.34   $218.35   $218.30  
  Purchase #3 $166.70   6.542%   $177.6055   $177.61   $177.60   $177.60  
  Purchase #4 $91.90   11.296%   $102.281   $102.28   $102.30   $102.30  
  Purchase #5 $74.76   10.333%   $82.485   $82.49   $82.50   $82.50  
  Purchase #6 $44.88   12.678%   $50.5699   $50.57   $50.55   $50.60  
  Purchase #7 $79.43   8.210%   $85.9512   $85.95   $85.95   $86.00  
  7 purchase totals = $786.54       $863.2381   $863.25   $863.25   $863.30