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 $92.38   7.135%   $98.9713   $98.97   $98.95   $99.00  
  Purchase #2 $115.55   3.547%   $119.6486   $119.65   $119.65   $119.60  
  Purchase #3 $60.99   7.390%   $65.4972   $65.50   $65.50   $65.50  
  Purchase #4 $101.32   6.499%   $107.9048   $107.90   $107.90   $107.90  
  Purchase #5 $62.80   12.244%   $70.4892   $70.49   $70.50   $70.50  
  Purchase #6 $125.75   7.186%   $134.7864   $134.79   $134.80   $134.80  
  Purchase #7 $185.56   10.492%   $205.029   $205.03   $205.05   $205.00  
  7 purchase totals = $744.35       $802.3265   $802.33   $802.35   $802.30