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	$139.39	12.380%	$156.6465	$156.65	$156.65	$156.60
Purchase #2	$126.74	13.344%	$143.6522	$143.65	$143.65	$143.70
Purchase #3	$59.80	4.755%	$62.6435	$62.64	$62.65	$62.60
Purchase #4	$18.29	5.490%	$19.2941	$19.29	$19.30	$19.30
Purchase #5	$35.37	6.451%	$37.6517	$37.65	$37.65	$37.70
Purchase #6	$160.30	3.423%	$165.7871	$165.79	$165.80	$165.80
Purchase #7	$50.90	11.873%	$56.9434	$56.94	$56.95	$56.90
7 purchase totals =	$590.79		$642.6185	$642.61	$642.65	$642.60