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	$133.46	7.574%	$143.5683	$143.57	$143.55	$143.60
Purchase #2	$13.61	12.459%	$15.3057	$15.31	$15.30	$15.30
Purchase #3	$196.45	13.301%	$222.5798	$222.58	$222.60	$222.60
Purchase #4	$15.42	4.561%	$16.1233	$16.12	$16.10	$16.10
Purchase #5	$145.72	3.535%	$150.8712	$150.87	$150.85	$150.90
Purchase #6	$60.40	6.339%	$64.2288	$64.23	$64.25	$64.20
Purchase #7	$42.46	12.617%	$47.8172	$47.82	$47.80	$47.80
7 purchase totals =	$607.52		$660.4943	$660.50	$660.45	$660.50