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	$97.27	6.200%	$103.3007	$103.30	$103.30	$103.30
Purchase #2	$188.81	13.410%	$214.1294	$214.13	$214.15	$214.10
Purchase #3	$77.91	10.247%	$85.8934	$85.89	$85.90	$85.90
Purchase #4	$121.74	11.257%	$135.4443	$135.44	$135.45	$135.40
Purchase #5	$138.83	6.348%	$147.6429	$147.64	$147.65	$147.60
Purchase #6	$224.78	6.123%	$238.5433	$238.54	$238.55	$238.50
Purchase #7	$90.59	12.152%	$101.5985	$101.60	$101.60	$101.60
7 purchase totals =	$939.93		$1,026.5525	$1,026.54	$1,026.60	$1,026.40