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 $48.89   3.257%   $50.4823   $50.48   $50.50   $50.50  
  Purchase #2 $208.99   4.477%   $218.3465   $218.35   $218.35   $218.30  
  Purchase #3 $95.65   6.221%   $101.6004   $101.60   $101.60   $101.60  
  Purchase #4 $190.56   4.695%   $199.5068   $199.51   $199.50   $199.50  
  Purchase #5 $205.30   12.802%   $231.5825   $231.58   $231.60   $231.60  
  Purchase #6 $110.39   5.690%   $116.6712   $116.67   $116.65   $116.70  
  Purchase #7 $78.28   3.135%   $80.7341   $80.73   $80.75   $80.70  
  7 purchase totals = $938.06       $998.9238   $998.92   $998.95   $998.90