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 $141.38   3.185%   $145.883   $145.88   $145.90   $145.90  
  Purchase #2 $94.38   3.584%   $97.7626   $97.76   $97.75   $97.80  
  Purchase #3 $118.76   4.797%   $124.4569   $124.46   $124.45   $124.50  
  Purchase #4 $133.74   11.340%   $148.9061   $148.91   $148.90   $148.90  
  Purchase #5 $185.56   12.414%   $208.5954   $208.60   $208.60   $208.60  
  Purchase #6 $29.48   5.834%   $31.1999   $31.20   $31.20   $31.20  
  Purchase #7 $191.42   5.802%   $202.5262   $202.53   $202.55   $202.50  
  7 purchase totals = $894.72       $959.3301   $959.34   $959.35   $959.40