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	$74.51	5.709%	$78.7638	$78.76	$78.75	$78.80
Purchase #2	$67.99	12.482%	$76.4765	$76.48	$76.50	$76.50
Purchase #3	$75.54	10.577%	$83.5299	$83.53	$83.55	$83.50
Purchase #4	$40.75	11.649%	$45.497	$45.50	$45.50	$45.50
Purchase #5	$14.65	11.426%	$16.3239	$16.32	$16.30	$16.30
Purchase #6	$107.82	9.266%	$117.8106	$117.81	$117.80	$117.80
Purchase #7	$38.91	3.622%	$40.3193	$40.32	$40.30	$40.30
7 purchase totals =	$420.17		$458.7210	$458.72	$458.70	$458.70