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 $204.65   3.469%   $211.7493   $211.75   $211.75   $211.70  
  Purchase #2 $110.39   8.428%   $119.6937   $119.69   $119.70   $119.70  
  Purchase #3 $66.65   4.713%   $69.7912   $69.79   $69.80   $69.80  
  Purchase #4 $51.37   3.500%   $53.168   $53.17   $53.15   $53.20  
  Purchase #5 $71.59   7.622%   $77.0466   $77.05   $77.05   $77.00  
  Purchase #6 $153.28   6.304%   $162.9428   $162.94   $162.95   $162.90  
  Purchase #7 $114.30   13.200%   $129.3876   $129.39   $129.40   $129.40  
  7 purchase totals = $772.23       $823.7792   $823.78   $823.80   $823.70