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	$115.72	4.551%	$120.9864	$120.99	$121.00	$121.00
Purchase #2	$169.57	11.230%	$188.6127	$188.61	$188.60	$188.60
Purchase #3	$173.25	13.198%	$196.1155	$196.12	$196.10	$196.10
Purchase #4	$184.64	6.217%	$196.1191	$196.12	$196.10	$196.10
Purchase #5	$59.52	3.257%	$61.4586	$61.46	$61.45	$61.50
Purchase #6	$179.47	3.321%	$185.4302	$185.43	$185.45	$185.40
Purchase #7	$164.85	6.842%	$176.129	$176.13	$176.15	$176.10
7 purchase totals =	$1,047.02		$1,124.8515	$1,124.86	$1,124.85	$1,124.80