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	$53.78	10.306%	$59.3226	$59.32	$59.30	$59.30
Purchase #2	$56.55	5.446%	$59.6297	$59.63	$59.65	$59.60
Purchase #3	$233.49	9.652%	$256.0265	$256.03	$256.05	$256.00
Purchase #4	$133.95	6.238%	$142.3058	$142.31	$142.30	$142.30
Purchase #5	$15.92	13.112%	$18.0074	$18.01	$18.00	$18.00
Purchase #6	$124.81	12.578%	$140.5086	$140.51	$140.50	$140.50
Purchase #7	$183.95	11.707%	$205.485	$205.49	$205.50	$205.50
7 purchase totals =	$802.45		$881.2856	$881.30	$881.30	$881.20