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 $67.41   11.868%   $75.4102   $75.41   $75.40   $75.40  
  Purchase #2 $88.65   7.106%   $94.9495   $94.95   $94.95   $94.90  
  Purchase #3 $190.45   5.320%   $200.5819   $200.58   $200.60   $200.60  
  Purchase #4 $246.45   8.635%   $267.731   $267.73   $267.75   $267.70  
  Purchase #5 $20.53   5.569%   $21.6733   $21.67   $21.65   $21.70  
  Purchase #6 $68.89   4.259%   $71.824   $71.82   $71.80   $71.80  
  Purchase #7 $182.61   7.329%   $195.9935   $195.99   $196.00   $196.00  
  7 purchase totals = $864.99       $928.1634   $928.15   $928.15   $928.10