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	$157.40	8.640%	$170.9994	$171.00	$171.00	$171.00
Purchase #2	$78.91	13.529%	$89.5857	$89.59	$89.60	$89.60
Purchase #3	$147.82	13.743%	$168.1349	$168.13	$168.15	$168.10
Purchase #4	$204.38	11.117%	$227.1009	$227.10	$227.10	$227.10
Purchase #5	$15.70	8.423%	$17.0224	$17.02	$17.00	$17.00
Purchase #6	$18.27	11.111%	$20.3	$20.30	$20.30	$20.30
Purchase #7	$129.38	8.629%	$140.5442	$140.54	$140.55	$140.50
7 purchase totals =	$751.86		$833.6875	$833.68	$833.70	$833.60