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	$26.68	6.675%	$28.4609	$28.46	$28.45	$28.50
Purchase #2	$44.48	12.441%	$50.0138	$50.01	$50.00	$50.00
Purchase #3	$222.85	9.422%	$243.8469	$243.85	$243.85	$243.80
Purchase #4	$50.26	9.397%	$54.9829	$54.98	$55.00	$55.00
Purchase #5	$210.29	11.612%	$234.7089	$234.71	$234.70	$234.70
Purchase #6	$152.81	4.376%	$159.497	$159.50	$159.50	$159.50
Purchase #7	$143.52	5.215%	$151.0046	$151.00	$151.00	$151.00
7 purchase totals =	$850.89		$922.5150	$922.51	$922.50	$922.50