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 $76.99   8.626%   $83.6312   $83.63   $83.65   $83.60  
  Purchase #2 $99.57   6.695%   $106.2362   $106.24   $106.25   $106.20  
  Purchase #3 $141.82   6.164%   $150.5618   $150.56   $150.55   $150.60  
  Purchase #4 $40.51   7.259%   $43.4506   $43.45   $43.45   $43.50  
  Purchase #5 $185.78   11.717%   $207.5478   $207.55   $207.55   $207.50  
  Purchase #6 $226.67   4.172%   $236.1267   $236.13   $236.15   $236.10  
  Purchase #7 $44.27   10.726%   $49.0184   $49.02   $49.00   $49.00  
  7 purchase totals = $815.61       $876.5727   $876.58   $876.60   $876.50