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	$40.94	3.802%	$42.4965	$42.50	$42.50	$42.50
Purchase #2	$118.92	10.692%	$131.6349	$131.63	$131.65	$131.60
Purchase #3	$140.83	8.721%	$153.1118	$153.11	$153.10	$153.10
Purchase #4	$72.89	5.179%	$76.665	$76.67	$76.65	$76.70
Purchase #5	$153.89	7.486%	$165.4102	$165.41	$165.40	$165.40
Purchase #6	$183.61	8.314%	$198.8753	$198.88	$198.90	$198.90
Purchase #7	$175.68	5.437%	$185.2317	$185.23	$185.25	$185.20
7 purchase totals =	$886.76		$953.4254	$953.43	$953.45	$953.40