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 $232.98   5.525%   $245.8521   $245.85   $245.85   $245.90  
  Purchase #2 $103.88   6.536%   $110.6696   $110.67   $110.65   $110.70  
  Purchase #3 $75.39   13.111%   $85.2744   $85.27   $85.25   $85.30  
  Purchase #4 $95.61   9.407%   $104.604   $104.60   $104.60   $104.60  
  Purchase #5 $124.96   7.140%   $133.8821   $133.88   $133.90   $133.90  
  Purchase #6 $58.71   5.588%   $61.9907   $61.99   $62.00   $62.00  
  Purchase #7 $53.49   11.725%   $59.7617   $59.76   $59.75   $59.80  
  7 purchase totals = $745.02       $802.0346   $802.02   $802.00   $802.20