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	$196.82	3.647%	$203.998	$204.00	$204.00	$204.00
Purchase #2	$230.74	3.442%	$238.6821	$238.68	$238.70	$238.70
Purchase #3	$38.27	6.497%	$40.7564	$40.76	$40.75	$40.80
Purchase #4	$74.90	11.451%	$83.4768	$83.48	$83.50	$83.50
Purchase #5	$37.62	6.657%	$40.1244	$40.12	$40.10	$40.10
Purchase #6	$187.72	10.859%	$208.1045	$208.10	$208.10	$208.10
Purchase #7	$102.31	13.496%	$116.1178	$116.12	$116.10	$116.10
7 purchase totals =	$868.38		$931.2600	$931.26	$931.25	$931.30