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	$148.37	11.322%	$165.1685	$165.17	$165.15	$165.20
Purchase #2	$24.32	12.707%	$27.4103	$27.41	$27.40	$27.40
Purchase #3	$247.75	4.505%	$258.9111	$258.91	$258.90	$258.90
Purchase #4	$43.34	4.250%	$45.182	$45.18	$45.20	$45.20
Purchase #5	$79.75	4.772%	$83.5557	$83.56	$83.55	$83.60
Purchase #6	$37.36	12.517%	$42.0364	$42.04	$42.05	$42.00
Purchase #7	$216.63	11.527%	$241.6009	$241.60	$241.60	$241.60
7 purchase totals =	$797.52		$863.8649	$863.87	$863.85	$863.90