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	$228.46	12.292%	$256.5423	$256.54	$256.55	$256.50
Purchase #2	$232.57	13.622%	$264.2507	$264.25	$264.25	$264.30
Purchase #3	$26.86	10.640%	$29.7179	$29.72	$29.70	$29.70
Purchase #4	$147.41	6.351%	$156.772	$156.77	$156.75	$156.80
Purchase #5	$55.53	6.355%	$59.0589	$59.06	$59.05	$59.10
Purchase #6	$90.26	11.236%	$100.4016	$100.40	$100.40	$100.40
Purchase #7	$24.35	3.109%	$25.107	$25.11	$25.10	$25.10
7 purchase totals =	$805.44		$891.8504	$891.85	$891.80	$891.90