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	$79.30	13.846%	$90.2799	$90.28	$90.30	$90.30
Purchase #2	$80.66	12.764%	$90.9554	$90.96	$90.95	$91.00
Purchase #3	$138.25	11.787%	$154.5455	$154.55	$154.55	$154.50
Purchase #4	$52.64	5.115%	$55.3325	$55.33	$55.35	$55.30
Purchase #5	$228.89	10.343%	$252.5641	$252.56	$252.55	$252.60
Purchase #6	$54.86	8.126%	$59.3179	$59.32	$59.30	$59.30
Purchase #7	$49.64	8.823%	$54.0197	$54.02	$54.00	$54.00
7 purchase totals =	$684.24		$757.0150	$757.02	$757.00	$757.00