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 $59.72   4.228%   $62.245   $62.25   $62.25   $62.20  
  Purchase #2 $6.40   7.226%   $6.8625   $6.86   $6.85   $6.90  
  Purchase #3 $21.74   5.199%   $22.8703   $22.87   $22.85   $22.90  
  Purchase #4 $230.95   4.153%   $240.5414   $240.54   $240.55   $240.50  
  Purchase #5 $43.44   8.831%   $47.2762   $47.28   $47.30   $47.30  
  Purchase #6 $90.59   13.699%   $102.9999   $103.00   $103.00   $103.00  
  Purchase #7 $120.85   13.320%   $136.9472   $136.95   $136.95   $136.90  
  7 purchase totals = $573.69       $619.7425   $619.75   $619.75   $619.70