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	$122.88	11.863%	$137.4573	$137.46	$137.45	$137.50
Purchase #2	$63.60	3.392%	$65.7573	$65.76	$65.75	$65.80
Purchase #3	$243.36	10.182%	$268.1389	$268.14	$268.15	$268.10
Purchase #4	$83.38	11.445%	$92.9228	$92.92	$92.90	$92.90
Purchase #5	$244.38	6.396%	$260.0105	$260.01	$260.00	$260.00
Purchase #6	$81.61	8.510%	$88.555	$88.56	$88.55	$88.60
Purchase #7	$140.60	12.797%	$158.5926	$158.59	$158.60	$158.60
7 purchase totals =	$979.81		$1,071.4344	$1,071.44	$1,071.40	$1,071.50