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	$70.32	12.174%	$78.8808	$78.88	$78.90	$78.90
Purchase #2	$55.88	12.308%	$62.7577	$62.76	$62.75	$62.80
Purchase #3	$199.70	8.135%	$215.9456	$215.95	$215.95	$215.90
Purchase #4	$153.66	7.427%	$165.0723	$165.07	$165.05	$165.10
Purchase #5	$50.35	13.854%	$57.3255	$57.33	$57.35	$57.30
Purchase #6	$76.45	5.547%	$80.6907	$80.69	$80.70	$80.70
Purchase #7	$37.57	6.835%	$40.1379	$40.14	$40.15	$40.10
7 purchase totals =	$643.93		$700.8105	$700.82	$700.85	$700.80