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 $66.99   12.253%   $75.1983   $75.20   $75.20   $75.20  
  Purchase #2 $85.81   6.450%   $91.3447   $91.34   $91.35   $91.30  
  Purchase #3 $154.54   9.237%   $168.8149   $168.81   $168.80   $168.80  
  Purchase #4 $175.37   10.376%   $193.5664   $193.57   $193.55   $193.60  
  Purchase #5 $183.81   11.815%   $205.5272   $205.53   $205.55   $205.50  
  Purchase #6 $69.69   8.680%   $75.7391   $75.74   $75.75   $75.70  
  Purchase #7 $15.47   11.355%   $17.2266   $17.23   $17.25   $17.20  
  7 purchase totals = $751.68       $827.4172   $827.42   $827.45   $827.30