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	$195.99	13.582%	$222.6094	$222.61	$222.60	$222.60
Purchase #2	$34.35	10.403%	$37.9234	$37.92	$37.90	$37.90
Purchase #3	$122.90	12.206%	$137.9012	$137.90	$137.90	$137.90
Purchase #4	$115.50	4.612%	$120.8269	$120.83	$120.85	$120.80
Purchase #5	$84.39	13.832%	$96.0628	$96.06	$96.05	$96.10
Purchase #6	$39.90	9.275%	$43.6007	$43.60	$43.60	$43.60
Purchase #7	$112.49	8.687%	$122.262	$122.26	$122.25	$122.30
7 purchase totals =	$705.52		$781.1864	$781.18	$781.15	$781.20