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 $213.34   11.865%   $238.6528   $238.65   $238.65   $238.70  
  Purchase #2 $90.81   4.541%   $94.9337   $94.93   $94.95   $94.90  
  Purchase #3 $185.60   9.243%   $202.755   $202.76   $202.75   $202.80  
  Purchase #4 $62.97   6.202%   $66.8754   $66.88   $66.90   $66.90  
  Purchase #5 $97.53   11.597%   $108.8406   $108.84   $108.85   $108.80  
  Purchase #6 $208.90   5.555%   $220.5044   $220.50   $220.50   $220.50  
  Purchase #7 $49.40   11.842%   $55.2499   $55.25   $55.25   $55.20  
  7 purchase totals = $908.55       $987.8118   $987.81   $987.85   $987.80