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 $89.95   7.406%   $96.6117   $96.61   $96.60   $96.60  
  Purchase #2 $109.38   5.694%   $115.6081   $115.61   $115.60   $115.60  
  Purchase #3 $242.27   3.260%   $250.168   $250.17   $250.15   $250.20  
  Purchase #4 $180.72   7.515%   $194.3011   $194.30   $194.30   $194.30  
  Purchase #5 $190.49   10.649%   $210.7753   $210.78   $210.80   $210.80  
  Purchase #6 $106.96   8.512%   $116.0644   $116.06   $116.05   $116.10  
  Purchase #7 $229.62   5.860%   $243.0757   $243.08   $243.10   $243.10  
  7 purchase totals = $1,149.39       $1,226.6043   $1,226.61   $1,226.60   $1,226.70