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	$113.63	6.792%	$121.3477	$121.35	$121.35	$121.30
Purchase #2	$37.31	13.542%	$42.3625	$42.36	$42.35	$42.40
Purchase #3	$87.41	4.548%	$91.3854	$91.39	$91.40	$91.40
Purchase #4	$127.29	13.418%	$144.3698	$144.37	$144.35	$144.40
Purchase #5	$69.69	3.762%	$72.3117	$72.31	$72.30	$72.30
Purchase #6	$232.52	5.784%	$245.969	$245.97	$245.95	$246.00
Purchase #7	$40.76	13.824%	$46.3947	$46.39	$46.40	$46.40
7 purchase totals =	$708.61		$764.1408	$764.14	$764.10	$764.20