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 $12.29   3.189%   $12.6819   $12.68   $12.70   $12.70  
  Purchase #2 $105.85   6.263%   $112.4794   $112.48   $112.50   $112.50  
  Purchase #3 $7.73   9.517%   $8.4657   $8.47   $8.45   $8.50  
  Purchase #4 $47.34   9.388%   $51.7843   $51.78   $51.80   $51.80  
  Purchase #5 $158.28   5.360%   $166.7638   $166.76   $166.75   $166.80  
  Purchase #6 $115.39   4.152%   $120.181   $120.18   $120.20   $120.20  
  Purchase #7 $217.67   7.378%   $233.7297   $233.73   $233.75   $233.70  
  7 purchase totals = $664.55       $706.0858   $706.08   $706.15   $706.20