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	$62.75	6.340%	$66.7284	$66.73	$66.75	$66.70
Purchase #2	$78.32	6.170%	$83.1523	$83.15	$83.15	$83.20
Purchase #3	$42.26	6.748%	$45.1117	$45.11	$45.10	$45.10
Purchase #4	$80.33	13.753%	$91.3778	$91.38	$91.40	$91.40
Purchase #5	$223.90	10.526%	$247.4677	$247.47	$247.45	$247.50
Purchase #6	$17.29	9.550%	$18.9412	$18.94	$18.95	$18.90
Purchase #7	$11.87	4.451%	$12.3983	$12.40	$12.40	$12.40
7 purchase totals =	$516.72		$565.1774	$565.18	$565.20	$565.20