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	$74.83	9.645%	$82.0474	$82.05	$82.05	$82.00
Purchase #2	$100.82	4.280%	$105.1351	$105.14	$105.15	$105.10
Purchase #3	$95.99	13.836%	$109.2712	$109.27	$109.25	$109.30
Purchase #4	$216.89	9.213%	$236.8721	$236.87	$236.85	$236.90
Purchase #5	$129.37	6.160%	$137.3392	$137.34	$137.35	$137.30
Purchase #6	$96.51	13.531%	$109.5688	$109.57	$109.55	$109.60
Purchase #7	$26.98	9.131%	$29.4435	$29.44	$29.45	$29.40
7 purchase totals =	$741.39		$809.6773	$809.68	$809.65	$809.60