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	$159.30	3.275%	$164.5171	$164.52	$164.50	$164.50
Purchase #2	$87.56	4.705%	$91.6797	$91.68	$91.70	$91.70
Purchase #3	$75.49	13.732%	$85.8563	$85.86	$85.85	$85.90
Purchase #4	$227.43	12.696%	$256.3045	$256.30	$256.30	$256.30
Purchase #5	$129.36	13.328%	$146.6011	$146.60	$146.60	$146.60
Purchase #6	$16.69	9.408%	$18.2602	$18.26	$18.25	$18.30
Purchase #7	$133.51	9.819%	$146.6193	$146.62	$146.60	$146.60
7 purchase totals =	$829.34		$909.8382	$909.84	$909.80	$909.90