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	$71.57	12.482%	$80.5034	$80.50	$80.50	$80.50
Purchase #2	$189.33	10.315%	$208.8594	$208.86	$208.85	$208.90
Purchase #3	$71.45	11.837%	$79.9075	$79.91	$79.90	$79.90
Purchase #4	$117.34	4.474%	$122.5898	$122.59	$122.60	$122.60
Purchase #5	$29.56	5.808%	$31.2768	$31.28	$31.30	$31.30
Purchase #6	$51.97	6.657%	$55.4296	$55.43	$55.45	$55.40
Purchase #7	$158.72	4.368%	$165.6529	$165.65	$165.65	$165.70
7 purchase totals =	$689.94		$744.2194	$744.22	$744.25	$744.30