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	$113.34	13.269%	$128.3791	$128.38	$128.40	$128.40
Purchase #2	$176.77	7.698%	$190.3778	$190.38	$190.40	$190.40
Purchase #3	$243.40	6.871%	$260.124	$260.12	$260.10	$260.10
Purchase #4	$139.52	6.401%	$148.4507	$148.45	$148.45	$148.50
Purchase #5	$139.47	7.747%	$150.2747	$150.27	$150.25	$150.30
Purchase #6	$230.48	3.649%	$238.8902	$238.89	$238.90	$238.90
Purchase #7	$21.28	4.626%	$22.2644	$22.26	$22.25	$22.30
7 purchase totals =	$1,064.26		$1,138.7609	$1,138.75	$1,138.75	$1,138.90