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 $69.77   9.297%   $76.2565   $76.26   $76.25   $76.30  
  Purchase #2 $162.42   12.431%   $182.6104   $182.61   $182.60   $182.60  
  Purchase #3 $145.94   10.224%   $160.8609   $160.86   $160.85   $160.90  
  Purchase #4 $22.93   8.716%   $24.9286   $24.93   $24.95   $24.90  
  Purchase #5 $19.35   11.827%   $21.6385   $21.64   $21.65   $21.60  
  Purchase #6 $232.26   7.133%   $248.8271   $248.83   $248.85   $248.80  
  Purchase #7 $249.65   7.718%   $268.918   $268.92   $268.90   $268.90  
  7 purchase totals = $902.32       $984.0400   $984.05   $984.05   $984.00