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 $77.82   13.328%   $88.1918   $88.19   $88.20   $88.20  
  Purchase #2 $157.36   3.414%   $162.7323   $162.73   $162.75   $162.70  
  Purchase #3 $47.79   6.389%   $50.8433   $50.84   $50.85   $50.80  
  Purchase #4 $58.93   7.200%   $63.173   $63.17   $63.15   $63.20  
  Purchase #5 $147.67   10.827%   $163.6582   $163.66   $163.65   $163.70  
  Purchase #6 $72.76   4.343%   $75.92   $75.92   $75.90   $75.90  
  Purchase #7 $200.93   6.252%   $213.4921   $213.49   $213.50   $213.50  
  7 purchase totals = $763.26       $818.0107   $818.00   $818.00   $818.00