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	$167.37	10.730%	$185.3288	$185.33	$185.35	$185.30
Purchase #2	$159.75	3.697%	$165.656	$165.66	$165.65	$165.70
Purchase #3	$137.54	3.255%	$142.0169	$142.02	$142.00	$142.00
Purchase #4	$40.39	13.165%	$45.7073	$45.71	$45.70	$45.70
Purchase #5	$9.68	5.389%	$10.2017	$10.20	$10.20	$10.20
Purchase #6	$83.52	8.736%	$90.8163	$90.82	$90.80	$90.80
Purchase #7	$178.56	10.257%	$196.8749	$196.87	$196.85	$196.90
7 purchase totals =	$776.81		$836.6019	$836.61	$836.55	$836.60