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	$43.86	4.496%	$45.8319	$45.83	$45.85	$45.80
Purchase #2	$161.44	3.640%	$167.3164	$167.32	$167.30	$167.30
Purchase #3	$114.96	6.590%	$122.5359	$122.54	$122.55	$122.50
Purchase #4	$151.44	13.658%	$172.1237	$172.12	$172.10	$172.10
Purchase #5	$15.77	6.868%	$16.8531	$16.85	$16.85	$16.90
Purchase #6	$226.53	7.502%	$243.5243	$243.52	$243.50	$243.50
Purchase #7	$54.37	13.786%	$61.8654	$61.87	$61.85	$61.90
7 purchase totals =	$768.37		$830.0507	$830.05	$830.00	$830.00