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	$136.80	10.493%	$151.1544	$151.15	$151.15	$151.20
Purchase #2	$14.49	6.112%	$15.3756	$15.38	$15.40	$15.40
Purchase #3	$159.59	9.804%	$175.2362	$175.24	$175.25	$175.20
Purchase #4	$37.47	13.556%	$42.5494	$42.55	$42.55	$42.50
Purchase #5	$18.33	5.485%	$19.3354	$19.34	$19.35	$19.30
Purchase #6	$231.64	8.286%	$250.8337	$250.83	$250.85	$250.80
Purchase #7	$221.26	9.781%	$242.9014	$242.90	$242.90	$242.90
7 purchase totals =	$819.58		$897.3861	$897.39	$897.45	$897.30