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 $41.92   9.697%   $45.985   $45.99   $46.00   $46.00  
  Purchase #2 $172.46   11.388%   $192.0997   $192.10   $192.10   $192.10  
  Purchase #3 $20.82   9.443%   $22.786   $22.79   $22.80   $22.80  
  Purchase #4 $68.88   9.797%   $75.6282   $75.63   $75.65   $75.60  
  Purchase #5 $189.45   3.797%   $196.6434   $196.64   $196.65   $196.60  
  Purchase #6 $169.77   5.137%   $178.4911   $178.49   $178.50   $178.50  
  Purchase #7 $99.27   12.686%   $111.8634   $111.86   $111.85   $111.90  
  7 purchase totals = $762.57       $823.4968   $823.50   $823.55   $823.50