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	$165.63	3.358%	$171.1919	$171.19	$171.20	$171.20
Purchase #2	$36.40	3.183%	$37.5586	$37.56	$37.55	$37.60
Purchase #3	$155.35	8.394%	$168.3901	$168.39	$168.40	$168.40
Purchase #4	$179.92	11.481%	$200.5766	$200.58	$200.60	$200.60
Purchase #5	$65.62	10.140%	$72.2739	$72.27	$72.25	$72.30
Purchase #6	$133.77	8.750%	$145.4749	$145.47	$145.45	$145.50
Purchase #7	$191.34	3.170%	$197.4055	$197.41	$197.40	$197.40
7 purchase totals =	$928.03		$992.8715	$992.87	$992.85	$993.00