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	$240.81	3.617%	$249.5201	$249.52	$249.50	$249.50
Purchase #2	$50.78	13.258%	$57.5124	$57.51	$57.50	$57.50
Purchase #3	$90.33	10.734%	$100.026	$100.03	$100.05	$100.00
Purchase #4	$216.69	13.395%	$245.7156	$245.72	$245.70	$245.70
Purchase #5	$160.54	10.181%	$176.8846	$176.88	$176.90	$176.90
Purchase #6	$195.34	8.475%	$211.8951	$211.90	$211.90	$211.90
Purchase #7	$136.62	5.355%	$143.936	$143.94	$143.95	$143.90
7 purchase totals =	$1,091.11		$1,185.4898	$1,185.50	$1,185.50	$1,185.40