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	$244.50	6.111%	$259.4414	$259.44	$259.45	$259.40
Purchase #2	$79.56	5.252%	$83.7385	$83.74	$83.75	$83.70
Purchase #3	$37.29	13.536%	$42.3376	$42.34	$42.35	$42.30
Purchase #4	$16.80	4.571%	$17.5679	$17.57	$17.55	$17.60
Purchase #5	$34.71	13.578%	$39.4229	$39.42	$39.40	$39.40
Purchase #6	$50.57	12.485%	$56.8837	$56.88	$56.90	$56.90
Purchase #7	$147.82	12.162%	$165.7979	$165.80	$165.80	$165.80
7 purchase totals =	$611.25		$665.1899	$665.19	$665.20	$665.10