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	$90.45	10.613%	$100.0495	$100.05	$100.05	$100.00
Purchase #2	$124.69	13.792%	$141.8872	$141.89	$141.90	$141.90
Purchase #3	$230.48	5.621%	$243.4353	$243.44	$243.45	$243.40
Purchase #4	$203.46	13.752%	$231.4398	$231.44	$231.45	$231.40
Purchase #5	$148.37	8.160%	$160.477	$160.48	$160.50	$160.50
Purchase #6	$88.35	8.354%	$95.7308	$95.73	$95.75	$95.70
Purchase #7	$117.44	8.847%	$127.8299	$127.83	$127.85	$127.80
7 purchase totals =	$1,003.24		$1,100.8495	$1,100.86	$1,100.95	$1,100.70