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	$239.91	13.435%	$272.1419	$272.14	$272.15	$272.10
Purchase #2	$109.72	13.826%	$124.8899	$124.89	$124.90	$124.90
Purchase #3	$167.80	4.460%	$175.2839	$175.28	$175.30	$175.30
Purchase #4	$41.78	9.494%	$45.7466	$45.75	$45.75	$45.70
Purchase #5	$207.54	8.362%	$224.8945	$224.89	$224.90	$224.90
Purchase #6	$246.87	13.385%	$279.9135	$279.91	$279.90	$279.90
Purchase #7	$38.49	13.729%	$43.7743	$43.77	$43.75	$43.80
7 purchase totals =	$1,052.11		$1,166.6446	$1,166.63	$1,166.65	$1,166.60