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 $89.55   6.622%   $95.48   $95.48   $95.50   $95.50  
  Purchase #2 $83.44   5.341%   $87.8965   $87.90   $87.90   $87.90  
  Purchase #3 $72.99   11.707%   $81.5349   $81.53   $81.55   $81.50  
  Purchase #4 $95.77   4.266%   $99.8555   $99.86   $99.85   $99.90  
  Purchase #5 $112.35   6.298%   $119.4258   $119.43   $119.45   $119.40  
  Purchase #6 $78.60   5.345%   $82.8012   $82.80   $82.80   $82.80  
  Purchase #7 $200.75   4.602%   $209.9885   $209.99   $210.00   $210.00  
  7 purchase totals = $733.45       $776.9824   $776.99   $777.05   $777.00