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	$38.63	9.114%	$42.1507	$42.15	$42.15	$42.20
Purchase #2	$57.77	5.241%	$60.7977	$60.80	$60.80	$60.80
Purchase #3	$54.61	13.287%	$61.866	$61.87	$61.85	$61.90
Purchase #4	$187.79	5.590%	$198.2875	$198.29	$198.30	$198.30
Purchase #5	$105.30	4.350%	$109.8806	$109.88	$109.90	$109.90
Purchase #6	$55.30	8.178%	$59.8224	$59.82	$59.80	$59.80
Purchase #7	$234.66	12.713%	$264.4923	$264.49	$264.50	$264.50
7 purchase totals =	$734.06		$797.2972	$797.30	$797.30	$797.40