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 $218.78   12.757%   $246.6898   $246.69   $246.70   $246.70  
  Purchase #2 $166.39   13.555%   $188.9442   $188.94   $188.95   $188.90  
  Purchase #3 $95.56   11.146%   $106.2111   $106.21   $106.20   $106.20  
  Purchase #4 $224.60   5.361%   $236.6408   $236.64   $236.65   $236.60  
  Purchase #5 $138.84   3.755%   $144.0534   $144.05   $144.05   $144.10  
  Purchase #6 $241.85   12.335%   $271.6822   $271.68   $271.70   $271.70  
  Purchase #7 $250.58   7.824%   $270.1854   $270.19   $270.20   $270.20  
  7 purchase totals = $1,336.60       $1,464.4069   $1,464.40   $1,464.45   $1,464.40