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	$127.75	8.205%	$138.2319	$138.23	$138.25	$138.20
Purchase #2	$59.38	13.703%	$67.5168	$67.52	$67.50	$67.50
Purchase #3	$22.87	4.621%	$23.9268	$23.93	$23.95	$23.90
Purchase #4	$79.75	12.121%	$89.4165	$89.42	$89.40	$89.40
Purchase #5	$170.49	12.490%	$191.7842	$191.78	$191.80	$191.80
Purchase #6	$247.53	3.567%	$256.3594	$256.36	$256.35	$256.40
Purchase #7	$219.86	11.861%	$245.9376	$245.94	$245.95	$245.90
7 purchase totals =	$927.63		$1,013.1732	$1,013.18	$1,013.20	$1,013.10