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	$84.61	6.471%	$90.0851	$90.09	$90.10	$90.10
Purchase #2	$133.41	8.777%	$145.1194	$145.12	$145.10	$145.10
Purchase #3	$107.31	12.111%	$120.3063	$120.31	$120.30	$120.30
Purchase #4	$134.90	10.341%	$148.85	$148.85	$148.85	$148.90
Purchase #5	$193.26	10.751%	$214.0374	$214.04	$214.05	$214.00
Purchase #6	$86.27	4.354%	$90.0262	$90.03	$90.05	$90.00
Purchase #7	$14.89	6.694%	$15.8867	$15.89	$15.90	$15.90
7 purchase totals =	$754.65		$824.3111	$824.33	$824.35	$824.30