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	$111.85	7.566%	$120.3126	$120.31	$120.30	$120.30
Purchase #2	$226.95	11.873%	$253.8958	$253.90	$253.90	$253.90
Purchase #3	$213.69	9.292%	$233.5461	$233.55	$233.55	$233.50
Purchase #4	$161.54	7.842%	$174.208	$174.21	$174.20	$174.20
Purchase #5	$81.89	8.764%	$89.0668	$89.07	$89.05	$89.10
Purchase #6	$85.94	6.286%	$91.3422	$91.34	$91.35	$91.30
Purchase #7	$156.29	11.252%	$173.8758	$173.88	$173.90	$173.90
7 purchase totals =	$1,038.15		$1,136.2473	$1,136.26	$1,136.25	$1,136.20