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	$165.52	8.163%	$179.0314	$179.03	$179.05	$179.00
Purchase #2	$39.87	10.415%	$44.0225	$44.02	$44.00	$44.00
Purchase #3	$188.68	4.348%	$196.8838	$196.88	$196.90	$196.90
Purchase #4	$134.40	12.613%	$151.3519	$151.35	$151.35	$151.40
Purchase #5	$50.31	10.648%	$55.667	$55.67	$55.65	$55.70
Purchase #6	$143.61	4.480%	$150.0437	$150.04	$150.05	$150.00
Purchase #7	$202.76	5.487%	$213.8854	$213.89	$213.90	$213.90
7 purchase totals =	$925.15		$990.8857	$990.88	$990.90	$990.90