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	$37.96	4.245%	$39.5714	$39.57	$39.55	$39.60
Purchase #2	$215.72	6.867%	$230.5335	$230.53	$230.55	$230.50
Purchase #3	$78.52	8.362%	$85.0858	$85.09	$85.10	$85.10
Purchase #4	$81.83	9.549%	$89.6439	$89.64	$89.65	$89.60
Purchase #5	$218.68	3.408%	$226.1326	$226.13	$226.15	$226.10
Purchase #6	$238.63	3.710%	$247.4832	$247.48	$247.50	$247.50
Purchase #7	$223.57	10.355%	$246.7207	$246.72	$246.70	$246.70
7 purchase totals =	$1,094.91		$1,165.1711	$1,165.16	$1,165.20	$1,165.10