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 $83.84   10.395%   $92.5552   $92.56   $92.55   $92.60  
  Purchase #2 $224.43   5.588%   $236.9711   $236.97   $236.95   $237.00  
  Purchase #3 $167.53   3.215%   $172.9161   $172.92   $172.90   $172.90  
  Purchase #4 $192.57   5.252%   $202.6838   $202.68   $202.70   $202.70  
  Purchase #5 $54.35   12.817%   $61.316   $61.32   $61.30   $61.30  
  Purchase #6 $78.25   8.504%   $84.9044   $84.90   $84.90   $84.90  
  Purchase #7 $54.96   5.317%   $57.8822   $57.88   $57.90   $57.90  
  7 purchase totals = $855.93       $909.2288   $909.23   $909.20   $909.30