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	$87.31	13.385%	$98.9964	$99.00	$99.00	$99.00
Purchase #2	$13.62	3.609%	$14.1115	$14.11	$14.10	$14.10
Purchase #3	$23.46	3.498%	$24.2806	$24.28	$24.30	$24.30
Purchase #4	$180.71	8.822%	$196.6522	$196.65	$196.65	$196.70
Purchase #5	$124.38	13.487%	$141.1551	$141.16	$141.15	$141.20
Purchase #6	$200.93	13.709%	$228.4755	$228.48	$228.50	$228.50
Purchase #7	$57.50	4.126%	$59.8725	$59.87	$59.85	$59.90
7 purchase totals =	$687.91		$763.5438	$763.55	$763.55	$763.70