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	$156.86	9.860%	$172.3264	$172.33	$172.35	$172.30
Purchase #2	$18.92	8.106%	$20.4537	$20.45	$20.45	$20.50
Purchase #3	$136.31	10.610%	$150.7725	$150.77	$150.75	$150.80
Purchase #4	$148.65	3.254%	$153.4871	$153.49	$153.50	$153.50
Purchase #5	$50.48	13.335%	$57.2115	$57.21	$57.20	$57.20
Purchase #6	$12.61	11.383%	$14.0454	$14.05	$14.05	$14.00
Purchase #7	$72.99	8.689%	$79.3321	$79.33	$79.35	$79.30
7 purchase totals =	$596.82		$647.6287	$647.63	$647.65	$647.60