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	$166.51	8.685%	$180.9714	$180.97	$180.95	$181.00
Purchase #2	$142.65	6.201%	$151.4957	$151.50	$151.50	$151.50
Purchase #3	$250.54	7.766%	$269.9969	$270.00	$270.00	$270.00
Purchase #4	$179.69	9.314%	$196.4263	$196.43	$196.45	$196.40
Purchase #5	$9.62	12.500%	$10.8225	$10.82	$10.80	$10.80
Purchase #6	$16.61	11.162%	$18.464	$18.46	$18.45	$18.50
Purchase #7	$70.98	6.135%	$75.3346	$75.33	$75.35	$75.30
7 purchase totals =	$836.60		$903.5114	$903.51	$903.50	$903.50