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	$150.45	5.662%	$158.9685	$158.97	$158.95	$159.00
Purchase #2	$161.88	4.286%	$168.8182	$168.82	$168.80	$168.80
Purchase #3	$186.46	3.355%	$192.7157	$192.72	$192.70	$192.70
Purchase #4	$69.30	12.343%	$77.8537	$77.85	$77.85	$77.90
Purchase #5	$139.89	11.185%	$155.5367	$155.54	$155.55	$155.50
Purchase #6	$139.33	11.194%	$154.9266	$154.93	$154.95	$154.90
Purchase #7	$170.93	3.266%	$176.5126	$176.51	$176.50	$176.50
7 purchase totals =	$1,018.24		$1,085.3320	$1,085.34	$1,085.30	$1,085.30