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	$91.75	12.579%	$103.2912	$103.29	$103.30	$103.30
Purchase #2	$228.54	8.157%	$247.182	$247.18	$247.20	$247.20
Purchase #3	$34.80	5.197%	$36.6086	$36.61	$36.60	$36.60
Purchase #4	$172.37	12.754%	$194.3541	$194.35	$194.35	$194.40
Purchase #5	$137.31	6.820%	$146.6745	$146.67	$146.65	$146.70
Purchase #6	$125.50	13.262%	$142.1438	$142.14	$142.15	$142.10
Purchase #7	$125.27	5.121%	$131.6851	$131.69	$131.70	$131.70
7 purchase totals =	$915.54		$1,001.9393	$1,001.93	$1,001.95	$1,002.00