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	$53.51	4.197%	$55.7558	$55.76	$55.75	$55.80
Purchase #2	$158.31	10.334%	$174.6698	$174.67	$174.65	$174.70
Purchase #3	$108.67	3.185%	$112.1311	$112.13	$112.15	$112.10
Purchase #4	$98.57	13.105%	$111.4876	$111.49	$111.50	$111.50
Purchase #5	$66.49	12.618%	$74.8797	$74.88	$74.90	$74.90
Purchase #6	$174.78	11.841%	$195.4757	$195.48	$195.50	$195.50
Purchase #7	$113.79	3.424%	$117.6862	$117.69	$117.70	$117.70
7 purchase totals =	$774.12		$842.0859	$842.10	$842.15	$842.20