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	$78.69	5.504%	$83.0211	$83.02	$83.00	$83.00
Purchase #2	$228.81	10.855%	$253.6473	$253.65	$253.65	$253.60
Purchase #3	$141.60	13.544%	$160.7783	$160.78	$160.80	$160.80
Purchase #4	$127.64	7.753%	$137.5359	$137.54	$137.55	$137.50
Purchase #5	$145.51	13.225%	$164.7537	$164.75	$164.75	$164.80
Purchase #6	$168.32	13.616%	$191.2385	$191.24	$191.25	$191.20
Purchase #7	$57.66	4.521%	$60.2668	$60.27	$60.25	$60.30
7 purchase totals =	$948.23		$1,051.2416	$1,051.25	$1,051.25	$1,051.20