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 $87.43   11.784%   $97.7328   $97.73   $97.75   $97.70  
  Purchase #2 $139.97   8.590%   $151.9934   $151.99   $152.00   $152.00  
  Purchase #3 $166.71   4.304%   $173.8852   $173.89   $173.90   $173.90  
  Purchase #4 $124.44   7.366%   $133.6063   $133.61   $133.60   $133.60  
  Purchase #5 $205.54   8.630%   $223.2781   $223.28   $223.30   $223.30  
  Purchase #6 $136.78   8.343%   $148.1916   $148.19   $148.20   $148.20  
  Purchase #7 $131.90   5.727%   $139.4539   $139.45   $139.45   $139.50  
  7 purchase totals = $992.77       $1,068.1413   $1,068.14   $1,068.20   $1,068.20