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 $86.31   13.692%   $98.1276   $98.13   $98.15   $98.10  
  Purchase #2 $100.39   7.252%   $107.6703   $107.67   $107.65   $107.70  
  Purchase #3 $101.91   13.825%   $115.9991   $116.00   $116.00   $116.00  
  Purchase #4 $57.68   4.533%   $60.2946   $60.29   $60.30   $60.30  
  Purchase #5 $87.88   6.693%   $93.7618   $93.76   $93.75   $93.80  
  Purchase #6 $111.34   7.716%   $119.931   $119.93   $119.95   $119.90  
  Purchase #7 $229.34   13.164%   $259.5303   $259.53   $259.55   $259.50  
  7 purchase totals = $774.85       $855.3147   $855.31   $855.35   $855.30