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	$78.32	6.256%	$83.2197	$83.22	$83.20	$83.20
Purchase #2	$184.69	4.252%	$192.543	$192.54	$192.55	$192.50
Purchase #3	$125.44	5.830%	$132.7532	$132.75	$132.75	$132.80
Purchase #4	$39.26	11.663%	$43.8389	$43.84	$43.85	$43.80
Purchase #5	$80.98	10.640%	$89.5963	$89.60	$89.60	$89.60
Purchase #6	$131.80	4.586%	$137.8443	$137.84	$137.85	$137.80
Purchase #7	$221.78	8.396%	$240.4006	$240.40	$240.40	$240.40
7 purchase totals =	$862.27		$920.1960	$920.19	$920.20	$920.10