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	$53.41	7.810%	$57.5813	$57.58	$57.60	$57.60
Purchase #2	$91.62	9.747%	$100.5502	$100.55	$100.55	$100.60
Purchase #3	$112.60	10.610%	$124.5469	$124.55	$124.55	$124.50
Purchase #4	$55.40	11.513%	$61.7782	$61.78	$61.80	$61.80
Purchase #5	$56.92	7.692%	$61.2983	$61.30	$61.30	$61.30
Purchase #6	$56.28	8.851%	$61.2613	$61.26	$61.25	$61.30
Purchase #7	$240.71	13.517%	$273.2468	$273.25	$273.25	$273.20
7 purchase totals =	$666.94		$740.2630	$740.27	$740.30	$740.30