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 $65.94   11.438%   $73.4822   $73.48   $73.50   $73.50  
  Purchase #2 $71.35   3.344%   $73.7359   $73.74   $73.75   $73.70  
  Purchase #3 $23.83   10.452%   $26.3207   $26.32   $26.30   $26.30  
  Purchase #4 $232.57   4.447%   $242.9124   $242.91   $242.90   $242.90  
  Purchase #5 $236.75   10.214%   $260.9316   $260.93   $260.95   $260.90  
  Purchase #6 $245.45   6.145%   $260.5329   $260.53   $260.55   $260.50  
  Purchase #7 $216.30   9.495%   $236.8377   $236.84   $236.85   $236.80  
  7 purchase totals = $1,092.19       $1,174.7534   $1,174.75   $1,174.80   $1,174.60