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	$80.86	11.228%	$89.939	$89.94	$89.95	$89.90
Purchase #2	$246.66	7.224%	$264.4787	$264.48	$264.50	$264.50
Purchase #3	$88.78	3.699%	$92.064	$92.06	$92.05	$92.10
Purchase #4	$42.83	10.133%	$47.17	$47.17	$47.15	$47.20
Purchase #5	$207.86	13.450%	$235.8172	$235.82	$235.80	$235.80
Purchase #6	$41.54	7.235%	$44.5454	$44.55	$44.55	$44.50
Purchase #7	$202.70	9.255%	$221.4599	$221.46	$221.45	$221.50
7 purchase totals =	$911.23		$995.4742	$995.48	$995.45	$995.50