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	$17.49	6.693%	$18.6606	$18.66	$18.65	$18.70
Purchase #2	$160.51	12.629%	$180.7808	$180.78	$180.80	$180.80
Purchase #3	$159.79	5.714%	$168.9204	$168.92	$168.90	$168.90
Purchase #4	$142.76	3.199%	$147.3269	$147.33	$147.35	$147.30
Purchase #5	$136.65	5.450%	$144.0974	$144.10	$144.10	$144.10
Purchase #6	$132.55	9.130%	$144.6518	$144.65	$144.65	$144.70
Purchase #7	$82.74	8.756%	$89.9847	$89.98	$90.00	$90.00
7 purchase totals =	$832.49		$894.4226	$894.42	$894.45	$894.50