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	$159.60	3.219%	$164.7375	$164.74	$164.75	$164.70
Purchase #2	$10.48	13.741%	$11.9201	$11.92	$11.90	$11.90
Purchase #3	$123.39	13.564%	$140.1266	$140.13	$140.15	$140.10
Purchase #4	$41.80	7.847%	$45.08	$45.08	$45.10	$45.10
Purchase #5	$74.75	10.116%	$82.3117	$82.31	$82.30	$82.30
Purchase #6	$118.35	13.298%	$134.0882	$134.09	$134.10	$134.10
Purchase #7	$86.68	6.801%	$92.5751	$92.58	$92.60	$92.60
7 purchase totals =	$615.05		$670.8392	$670.85	$670.90	$670.80