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	$71.65	9.335%	$78.3385	$78.34	$78.35	$78.30
Purchase #2	$82.28	3.767%	$85.3795	$85.38	$85.40	$85.40
Purchase #3	$13.79	7.390%	$14.8091	$14.81	$14.80	$14.80
Purchase #4	$57.78	13.390%	$65.5167	$65.52	$65.50	$65.50
Purchase #5	$87.31	3.572%	$90.4287	$90.43	$90.45	$90.40
Purchase #6	$243.40	8.688%	$264.5466	$264.55	$264.55	$264.50
Purchase #7	$11.35	7.590%	$12.2115	$12.21	$12.20	$12.20
7 purchase totals =	$567.56		$611.2306	$611.24	$611.25	$611.10