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	$174.65	5.104%	$183.5641	$183.56	$183.55	$183.60
Purchase #2	$6.47	8.392%	$7.013	$7.01	$7.00	$7.00
Purchase #3	$87.74	13.777%	$99.8279	$99.83	$99.85	$99.80
Purchase #4	$59.79	10.730%	$66.2055	$66.21	$66.20	$66.20
Purchase #5	$50.62	6.194%	$53.7554	$53.76	$53.75	$53.80
Purchase #6	$35.76	12.755%	$40.3212	$40.32	$40.30	$40.30
Purchase #7	$80.80	8.568%	$87.7229	$87.72	$87.70	$87.70
7 purchase totals =	$495.83		$538.4100	$538.41	$538.35	$538.40