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	$102.30	7.141%	$109.6052	$109.61	$109.60	$109.60
Purchase #2	$228.87	10.846%	$253.6932	$253.69	$253.70	$253.70
Purchase #3	$230.27	11.420%	$256.5668	$256.57	$256.55	$256.60
Purchase #4	$235.72	4.496%	$246.318	$246.32	$246.30	$246.30
Purchase #5	$88.88	11.228%	$98.8594	$98.86	$98.85	$98.90
Purchase #6	$250.98	10.104%	$276.339	$276.34	$276.35	$276.30
Purchase #7	$133.30	10.293%	$147.0206	$147.02	$147.00	$147.00
7 purchase totals =	$1,270.32		$1,388.4022	$1,388.41	$1,388.35	$1,388.40