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	$75.26	12.409%	$84.599	$84.60	$84.60	$84.60
Purchase #2	$80.92	13.593%	$91.9195	$91.92	$91.90	$91.90
Purchase #3	$54.93	7.495%	$59.047	$59.05	$59.05	$59.00
Purchase #4	$174.46	11.634%	$194.7567	$194.76	$194.75	$194.80
Purchase #5	$52.46	10.221%	$57.8219	$57.82	$57.80	$57.80
Purchase #6	$238.71	8.184%	$258.246	$258.25	$258.25	$258.20
Purchase #7	$78.76	6.465%	$83.8518	$83.85	$83.85	$83.90
7 purchase totals =	$755.50		$830.2419	$830.25	$830.20	$830.20