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	$122.25	13.384%	$138.6119	$138.61	$138.60	$138.60
Purchase #2	$177.81	3.237%	$183.5657	$183.57	$183.55	$183.60
Purchase #3	$165.65	11.581%	$184.8339	$184.83	$184.85	$184.80
Purchase #4	$106.25	4.760%	$111.3075	$111.31	$111.30	$111.30
Purchase #5	$205.89	8.410%	$223.2053	$223.21	$223.20	$223.20
Purchase #6	$72.38	4.621%	$75.7247	$75.72	$75.70	$75.70
Purchase #7	$162.33	11.447%	$180.9119	$180.91	$180.90	$180.90
7 purchase totals =	$1,012.56		$1,098.1609	$1,098.16	$1,098.10	$1,098.10