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	$91.85	12.572%	$103.3974	$103.40	$103.40	$103.40
Purchase #2	$101.29	12.617%	$114.0698	$114.07	$114.05	$114.10
Purchase #3	$214.70	9.399%	$234.8797	$234.88	$234.90	$234.90
Purchase #4	$15.85	12.134%	$17.7732	$17.77	$17.75	$17.80
Purchase #5	$35.66	13.707%	$40.5479	$40.55	$40.55	$40.50
Purchase #6	$83.32	8.801%	$90.653	$90.65	$90.65	$90.70
Purchase #7	$135.94	10.526%	$150.249	$150.25	$150.25	$150.20
7 purchase totals =	$678.61		$751.5700	$751.57	$751.55	$751.60