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	$137.92	9.310%	$150.7604	$150.76	$150.75	$150.80
Purchase #2	$19.29	7.735%	$20.7821	$20.78	$20.80	$20.80
Purchase #3	$56.78	6.603%	$60.5292	$60.53	$60.55	$60.50
Purchase #4	$103.69	13.244%	$117.4227	$117.42	$117.40	$117.40
Purchase #5	$177.46	12.721%	$200.0347	$200.03	$200.05	$200.00
Purchase #6	$108.95	13.414%	$123.5646	$123.56	$123.55	$123.60
Purchase #7	$149.82	4.164%	$156.0585	$156.06	$156.05	$156.10
7 purchase totals =	$753.91		$829.1522	$829.14	$829.15	$829.20