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	$80.68	11.517%	$89.9719	$89.97	$89.95	$90.00
Purchase #2	$222.92	4.583%	$233.1364	$233.14	$233.15	$233.10
Purchase #3	$95.36	13.796%	$108.5159	$108.52	$108.50	$108.50
Purchase #4	$59.85	4.790%	$62.7168	$62.72	$62.70	$62.70
Purchase #5	$211.63	9.593%	$231.9317	$231.93	$231.95	$231.90
Purchase #6	$178.53	4.816%	$187.128	$187.13	$187.15	$187.10
Purchase #7	$53.91	12.460%	$60.6272	$60.63	$60.65	$60.60
7 purchase totals =	$902.88		$974.0279	$974.04	$974.05	$973.90