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	$51.61	10.740%	$57.1529	$57.15	$57.15	$57.20
Purchase #2	$135.36	3.847%	$140.5673	$140.57	$140.55	$140.60
Purchase #3	$154.35	4.609%	$161.464	$161.46	$161.45	$161.50
Purchase #4	$89.65	3.336%	$92.6407	$92.64	$92.65	$92.60
Purchase #5	$29.78	9.771%	$32.6898	$32.69	$32.70	$32.70
Purchase #6	$108.78	13.337%	$123.288	$123.29	$123.30	$123.30
Purchase #7	$228.90	4.252%	$238.6328	$238.63	$238.65	$238.60
7 purchase totals =	$798.43		$846.4355	$846.43	$846.45	$846.50