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 $182.38   11.582%   $203.5033   $203.50   $203.50   $203.50  
  Purchase #2 $94.38   7.165%   $101.1423   $101.14   $101.15   $101.10  
  Purchase #3 $58.65   6.202%   $62.2875   $62.29   $62.30   $62.30  
  Purchase #4 $130.34   11.157%   $144.882   $144.88   $144.90   $144.90  
  Purchase #5 $95.61   11.830%   $106.9207   $106.92   $106.90   $106.90  
  Purchase #6 $104.75   4.505%   $109.469   $109.47   $109.45   $109.50  
  Purchase #7 $247.99   8.702%   $269.5701   $269.57   $269.55   $269.60  
  7 purchase totals = $914.10       $997.7749   $997.77   $997.75   $997.80