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	$72.75	8.754%	$79.1185	$79.12	$79.10	$79.10
Purchase #2	$145.69	10.869%	$161.525	$161.53	$161.55	$161.50
Purchase #3	$42.69	7.454%	$45.8721	$45.87	$45.85	$45.90
Purchase #4	$101.98	3.528%	$105.5779	$105.58	$105.60	$105.60
Purchase #5	$203.75	9.207%	$222.5093	$222.51	$222.50	$222.50
Purchase #6	$244.33	3.854%	$253.7465	$253.75	$253.75	$253.70
Purchase #7	$113.93	8.750%	$123.8989	$123.90	$123.90	$123.90
7 purchase totals =	$925.12		$992.2482	$992.26	$992.25	$992.20