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	$246.94	11.168%	$274.5183	$274.52	$274.50	$274.50
Purchase #2	$155.41	3.842%	$161.3809	$161.38	$161.40	$161.40
Purchase #3	$91.55	9.244%	$100.0129	$100.01	$100.00	$100.00
Purchase #4	$204.48	7.594%	$220.0082	$220.01	$220.00	$220.00
Purchase #5	$12.74	6.219%	$13.5323	$13.53	$13.55	$13.50
Purchase #6	$95.86	4.799%	$100.4603	$100.46	$100.45	$100.50
Purchase #7	$88.72	11.243%	$98.6948	$98.69	$98.70	$98.70
7 purchase totals =	$895.70		$968.6077	$968.60	$968.60	$968.60