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	$58.28	4.707%	$61.0232	$61.02	$61.00	$61.00
Purchase #2	$26.72	9.254%	$29.1927	$29.19	$29.20	$29.20
Purchase #3	$115.41	11.718%	$128.9337	$128.93	$128.95	$128.90
Purchase #4	$188.41	4.204%	$196.3308	$196.33	$196.35	$196.30
Purchase #5	$40.56	4.817%	$42.5138	$42.51	$42.50	$42.50
Purchase #6	$135.40	13.532%	$153.7223	$153.72	$153.70	$153.70
Purchase #7	$195.69	11.759%	$218.7012	$218.70	$218.70	$218.70
7 purchase totals =	$760.47		$830.4177	$830.40	$830.40	$830.30