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 $62.75   5.103%   $65.9521   $65.95   $65.95   $66.00  
  Purchase #2 $58.37   9.498%   $63.914   $63.91   $63.90   $63.90  
  Purchase #3 $44.99   11.489%   $50.1589   $50.16   $50.15   $50.20  
  Purchase #4 $237.36   9.677%   $260.3293   $260.33   $260.35   $260.30  
  Purchase #5 $53.59   4.546%   $56.0262   $56.03   $56.05   $56.00  
  Purchase #6 $114.58   4.158%   $119.3442   $119.34   $119.35   $119.30  
  Purchase #7 $227.36   11.618%   $253.7747   $253.77   $253.75   $253.80  
  7 purchase totals = $799.00       $869.4994   $869.49   $869.50   $869.50