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	$138.94	5.328%	$146.3427	$146.34	$146.35	$146.30
Purchase #2	$211.82	7.847%	$228.4415	$228.44	$228.45	$228.40
Purchase #3	$38.43	13.104%	$43.4659	$43.47	$43.45	$43.50
Purchase #4	$83.29	8.764%	$90.5895	$90.59	$90.60	$90.60
Purchase #5	$79.31	8.130%	$85.7579	$85.76	$85.75	$85.80
Purchase #6	$156.72	3.603%	$162.3666	$162.37	$162.35	$162.40
Purchase #7	$106.37	3.611%	$110.211	$110.21	$110.20	$110.20
7 purchase totals =	$814.88		$867.1751	$867.18	$867.15	$867.20