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	$78.49	13.788%	$89.3122	$89.31	$89.30	$89.30
Purchase #2	$83.52	12.457%	$93.9241	$93.92	$93.90	$93.90
Purchase #3	$152.27	8.586%	$165.3439	$165.34	$165.35	$165.30
Purchase #4	$93.28	12.346%	$104.7963	$104.80	$104.80	$104.80
Purchase #5	$11.44	12.780%	$12.902	$12.90	$12.90	$12.90
Purchase #6	$75.40	10.500%	$83.317	$83.32	$83.30	$83.30
Purchase #7	$35.65	11.299%	$39.6781	$39.68	$39.70	$39.70
7 purchase totals =	$530.05		$589.2736	$589.27	$589.25	$589.20