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	$123.50	4.266%	$128.7685	$128.77	$128.75	$128.80
Purchase #2	$78.86	11.462%	$87.8989	$87.90	$87.90	$87.90
Purchase #3	$96.35	4.711%	$100.889	$100.89	$100.90	$100.90
Purchase #4	$183.37	5.800%	$194.0055	$194.01	$194.00	$194.00
Purchase #5	$15.79	5.200%	$16.6111	$16.61	$16.60	$16.60
Purchase #6	$159.34	7.640%	$171.5136	$171.51	$171.50	$171.50
Purchase #7	$200.58	5.104%	$210.8176	$210.82	$210.80	$210.80
7 purchase totals =	$857.79		$910.5042	$910.51	$910.45	$910.50