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	$18.97	6.712%	$20.2433	$20.24	$20.25	$20.20
Purchase #2	$104.38	10.848%	$115.7031	$115.70	$115.70	$115.70
Purchase #3	$53.83	12.321%	$60.4624	$60.46	$60.45	$60.50
Purchase #4	$12.51	3.749%	$12.979	$12.98	$13.00	$13.00
Purchase #5	$78.29	12.470%	$88.0528	$88.05	$88.05	$88.10
Purchase #6	$242.47	5.496%	$255.7962	$255.80	$255.80	$255.80
Purchase #7	$53.40	11.375%	$59.4743	$59.47	$59.45	$59.50
7 purchase totals =	$563.85		$612.7111	$612.70	$612.70	$612.80