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 $89.59   6.216%   $95.1589   $95.16   $95.15   $95.20  
  Purchase #2 $76.55   8.216%   $82.8393   $82.84   $82.85   $82.80  
  Purchase #3 $93.29   9.114%   $101.7925   $101.79   $101.80   $101.80  
  Purchase #4 $97.83   7.643%   $105.3071   $105.31   $105.30   $105.30  
  Purchase #5 $110.99   13.191%   $125.6307   $125.63   $125.65   $125.60  
  Purchase #6 $11.41   12.223%   $12.8046   $12.80   $12.80   $12.80  
  Purchase #7 $209.53   5.119%   $220.2558   $220.26   $220.25   $220.30  
  7 purchase totals = $689.19       $743.7889   $743.79   $743.80   $743.80