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	$37.91	12.685%	$42.7189	$42.72	$42.70	$42.70
Purchase #2	$221.35	5.337%	$233.1634	$233.16	$233.15	$233.20
Purchase #3	$243.57	12.613%	$274.2915	$274.29	$274.30	$274.30
Purchase #4	$186.79	13.655%	$212.2962	$212.30	$212.30	$212.30
Purchase #5	$49.47	3.831%	$51.3652	$51.37	$51.35	$51.40
Purchase #6	$32.98	4.120%	$34.3388	$34.34	$34.35	$34.30
Purchase #7	$81.67	10.479%	$90.2282	$90.23	$90.25	$90.20
7 purchase totals =	$853.74		$938.4022	$938.41	$938.40	$938.40