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	$75.70	3.491%	$78.3427	$78.34	$78.35	$78.30
Purchase #2	$57.75	3.448%	$59.7412	$59.74	$59.75	$59.70
Purchase #3	$129.77	7.723%	$139.7921	$139.79	$139.80	$139.80
Purchase #4	$118.26	10.110%	$130.2161	$130.22	$130.20	$130.20
Purchase #5	$80.64	10.107%	$88.7903	$88.79	$88.80	$88.80
Purchase #6	$105.83	8.770%	$115.1113	$115.11	$115.10	$115.10
Purchase #7	$39.96	7.376%	$42.9074	$42.91	$42.90	$42.90
7 purchase totals =	$607.91		$654.9011	$654.90	$654.90	$654.80