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	$150.97	7.228%	$161.8821	$161.88	$161.90	$161.90
Purchase #2	$83.38	5.692%	$88.126	$88.13	$88.15	$88.10
Purchase #3	$82.30	13.743%	$93.6105	$93.61	$93.60	$93.60
Purchase #4	$57.71	3.448%	$59.6998	$59.70	$59.70	$59.70
Purchase #5	$173.38	4.663%	$181.4647	$181.46	$181.45	$181.50
Purchase #6	$245.68	13.443%	$278.7068	$278.71	$278.70	$278.70
Purchase #7	$64.74	4.505%	$67.6565	$67.66	$67.65	$67.70
7 purchase totals =	$858.16		$931.1464	$931.15	$931.15	$931.20