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	$108.30	3.317%	$111.8923	$111.89	$111.90	$111.90
Purchase #2	$11.55	9.122%	$12.6036	$12.60	$12.60	$12.60
Purchase #3	$130.27	12.394%	$146.4157	$146.42	$146.40	$146.40
Purchase #4	$109.48	10.544%	$121.0236	$121.02	$121.00	$121.00
Purchase #5	$68.69	13.843%	$78.1988	$78.20	$78.20	$78.20
Purchase #6	$12.40	4.861%	$13.0028	$13.00	$13.00	$13.00
Purchase #7	$148.92	7.552%	$160.1664	$160.17	$160.15	$160.20
7 purchase totals =	$589.61		$643.3032	$643.30	$643.25	$643.30