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	$45.82	9.638%	$50.2361	$50.24	$50.25	$50.20
Purchase #2	$15.53	12.403%	$17.4562	$17.46	$17.45	$17.50
Purchase #3	$114.54	11.349%	$127.5391	$127.54	$127.55	$127.50
Purchase #4	$81.41	4.467%	$85.0466	$85.05	$85.05	$85.00
Purchase #5	$7.58	12.233%	$8.5073	$8.51	$8.50	$8.50
Purchase #6	$66.42	10.570%	$73.4406	$73.44	$73.45	$73.40
Purchase #7	$12.46	5.259%	$13.1153	$13.12	$13.10	$13.10
7 purchase totals =	$343.76		$375.3412	$375.36	$375.35	$375.20