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 $101.79   6.524%   $108.4308   $108.43   $108.45   $108.40  
  Purchase #2 $192.74   9.339%   $210.74   $210.74   $210.75   $210.70  
  Purchase #3 $46.88   3.550%   $48.5442   $48.54   $48.55   $48.50  
  Purchase #4 $84.93   12.261%   $95.3433   $95.34   $95.35   $95.30  
  Purchase #5 $165.60   10.117%   $182.3538   $182.35   $182.35   $182.40  
  Purchase #6 $178.51   13.515%   $202.6356   $202.64   $202.65   $202.60  
  Purchase #7 $10.62   7.420%   $11.408   $11.41   $11.40   $11.40  
  7 purchase totals = $781.07       $859.4557   $859.45   $859.50   $859.30