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 $95.51   5.776%   $101.0267   $101.03   $101.05   $101.00  
  Purchase #2 $147.96   7.873%   $159.6089   $159.61   $159.60   $159.60  
  Purchase #3 $95.59   9.532%   $104.7016   $104.70   $104.70   $104.70  
  Purchase #4 $151.93   7.589%   $163.46   $163.46   $163.45   $163.50  
  Purchase #5 $126.57   11.195%   $140.7395   $140.74   $140.75   $140.70  
  Purchase #6 $16.71   10.131%   $18.4029   $18.40   $18.40   $18.40  
  Purchase #7 $64.98   4.406%   $67.843   $67.84   $67.85   $67.80  
  7 purchase totals = $699.25       $755.7826   $755.78   $755.80   $755.70