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	$37.91	11.117%	$42.1245	$42.12	$42.10	$42.10
Purchase #2	$128.40	9.404%	$140.4747	$140.47	$140.45	$140.50
Purchase #3	$133.27	13.139%	$150.7803	$150.78	$150.80	$150.80
Purchase #4	$146.63	3.281%	$151.4409	$151.44	$151.45	$151.40
Purchase #5	$199.91	13.302%	$226.502	$226.50	$226.50	$226.50
Purchase #6	$21.72	11.479%	$24.2132	$24.21	$24.20	$24.20
Purchase #7	$147.72	10.119%	$162.6678	$162.67	$162.65	$162.70
7 purchase totals =	$815.56		$898.2034	$898.19	$898.15	$898.20