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	$130.83	3.482%	$135.3855	$135.39	$135.40	$135.40
Purchase #2	$101.89	3.205%	$105.1556	$105.16	$105.15	$105.20
Purchase #3	$126.47	8.350%	$137.0302	$137.03	$137.05	$137.00
Purchase #4	$109.33	12.762%	$123.2827	$123.28	$123.30	$123.30
Purchase #5	$55.42	10.841%	$61.4281	$61.43	$61.45	$61.40
Purchase #6	$42.91	3.851%	$44.5625	$44.56	$44.55	$44.60
Purchase #7	$172.34	13.853%	$196.2143	$196.21	$196.20	$196.20
7 purchase totals =	$739.19		$803.0589	$803.06	$803.10	$803.10