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 $187.54   4.417%   $195.8236   $195.82   $195.80   $195.80  
  Purchase #2 $92.37   6.297%   $98.1865   $98.19   $98.20   $98.20  
  Purchase #3 $152.36   6.480%   $162.2329   $162.23   $162.25   $162.20  
  Purchase #4 $40.59   3.693%   $42.089   $42.09   $42.10   $42.10  
  Purchase #5 $178.54   3.700%   $185.146   $185.15   $185.15   $185.10  
  Purchase #6 $11.51   12.200%   $12.9142   $12.91   $12.90   $12.90  
  Purchase #7 $81.74   4.116%   $85.1044   $85.10   $85.10   $85.10  
  7 purchase totals = $744.65       $781.4966   $781.49   $781.50   $781.40