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	$153.89	12.621%	$173.3125	$173.31	$173.30	$173.30
Purchase #2	$53.49	10.145%	$58.9166	$58.92	$58.90	$58.90
Purchase #3	$136.30	3.154%	$140.5989	$140.60	$140.60	$140.60
Purchase #4	$236.48	5.246%	$248.8857	$248.89	$248.90	$248.90
Purchase #5	$190.52	13.234%	$215.7334	$215.73	$215.75	$215.70
Purchase #6	$179.31	3.330%	$185.281	$185.28	$185.30	$185.30
Purchase #7	$172.47	5.460%	$181.8869	$181.89	$181.90	$181.90
7 purchase totals =	$1,122.46		$1,204.6150	$1,204.62	$1,204.65	$1,204.60