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	$120.93	13.474%	$137.2241	$137.22	$137.20	$137.20
Purchase #2	$175.67	8.762%	$191.0622	$191.06	$191.05	$191.10
Purchase #3	$138.63	9.813%	$152.2338	$152.23	$152.25	$152.20
Purchase #4	$149.27	7.271%	$160.1234	$160.12	$160.10	$160.10
Purchase #5	$82.42	8.141%	$89.1298	$89.13	$89.15	$89.10
Purchase #6	$13.25	6.483%	$14.109	$14.11	$14.10	$14.10
Purchase #7	$99.50	3.643%	$103.1248	$103.12	$103.10	$103.10
7 purchase totals =	$779.67		$847.0071	$846.99	$846.95	$846.90