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	8.287%	$105.3308	$105.33	$105.35	$105.30
Purchase #2	$90.68	9.230%	$99.0498	$99.05	$99.05	$99.00
Purchase #3	$244.52	3.686%	$253.533	$253.53	$253.55	$253.50
Purchase #4	$137.49	6.861%	$146.9232	$146.92	$146.90	$146.90
Purchase #5	$86.39	8.149%	$93.4299	$93.43	$93.45	$93.40
Purchase #6	$135.77	8.505%	$147.3172	$147.32	$147.30	$147.30
Purchase #7	$33.34	13.354%	$37.7922	$37.79	$37.80	$37.80
7 purchase totals =	$825.46		$883.3761	$883.37	$883.40	$883.20