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	$229.66	13.395%	$260.423	$260.42	$260.40	$260.40
Purchase #2	$59.89	10.347%	$66.0868	$66.09	$66.10	$66.10
Purchase #3	$63.72	5.394%	$67.1571	$67.16	$67.15	$67.20
Purchase #4	$218.59	12.135%	$245.1159	$245.12	$245.10	$245.10
Purchase #5	$48.48	12.597%	$54.587	$54.59	$54.60	$54.60
Purchase #6	$116.90	11.482%	$130.3225	$130.32	$130.30	$130.30
Purchase #7	$54.33	10.777%	$60.1851	$60.19	$60.20	$60.20
7 purchase totals =	$791.57		$883.8774	$883.89	$883.85	$883.90