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	$17.34	11.229%	$19.2871	$19.29	$19.30	$19.30
Purchase #2	$136.33	7.261%	$146.2289	$146.23	$146.25	$146.20
Purchase #3	$148.33	12.618%	$167.0463	$167.05	$167.05	$167.00
Purchase #4	$80.50	12.125%	$90.2606	$90.26	$90.25	$90.30
Purchase #5	$237.81	7.836%	$256.4448	$256.44	$256.45	$256.40
Purchase #6	$80.26	11.346%	$89.3663	$89.37	$89.35	$89.40
Purchase #7	$115.66	8.568%	$125.5697	$125.57	$125.55	$125.60
7 purchase totals =	$816.23		$894.2037	$894.21	$894.20	$894.20