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	$134.46	13.421%	$152.5059	$152.51	$152.50	$152.50
Purchase #2	$88.44	8.622%	$96.0653	$96.07	$96.05	$96.10
Purchase #3	$69.77	11.745%	$77.9645	$77.96	$77.95	$78.00
Purchase #4	$225.36	7.527%	$242.3228	$242.32	$242.30	$242.30
Purchase #5	$194.78	3.509%	$201.6148	$201.61	$201.60	$201.60
Purchase #6	$81.44	9.694%	$89.3348	$89.33	$89.35	$89.30
Purchase #7	$31.99	3.594%	$33.1397	$33.14	$33.15	$33.10
7 purchase totals =	$826.24		$892.9478	$892.94	$892.90	$892.90