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	$125.53	6.801%	$134.0673	$134.07	$134.05	$134.10
Purchase #2	$15.39	10.349%	$16.9827	$16.98	$17.00	$17.00
Purchase #3	$101.63	11.250%	$113.0634	$113.06	$113.05	$113.10
Purchase #4	$244.73	10.251%	$269.8173	$269.82	$269.80	$269.80
Purchase #5	$77.60	3.781%	$80.5341	$80.53	$80.55	$80.50
Purchase #6	$59.92	3.233%	$61.8572	$61.86	$61.85	$61.90
Purchase #7	$158.37	3.644%	$164.141	$164.14	$164.15	$164.10
7 purchase totals =	$783.17		$840.4630	$840.46	$840.45	$840.50