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 $65.59   12.427%   $73.7409   $73.74   $73.75   $73.70  
  Purchase #2 $30.25   11.441%   $33.7109   $33.71   $33.70   $33.70  
  Purchase #3 $250.89   11.638%   $280.0886   $280.09   $280.10   $280.10  
  Purchase #4 $144.61   12.333%   $162.4448   $162.44   $162.45   $162.40  
  Purchase #5 $205.48   5.267%   $216.3026   $216.30   $216.30   $216.30  
  Purchase #6 $169.34   10.213%   $186.6347   $186.63   $186.65   $186.60  
  Purchase #7 $232.75   9.512%   $254.8892   $254.89   $254.90   $254.90  
  7 purchase totals = $1,098.91       $1,207.8117   $1,207.80   $1,207.85   $1,207.70