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	$44.50	13.721%	$50.6058	$50.61	$50.60	$50.60
Purchase #2	$125.62	7.218%	$134.6873	$134.69	$134.70	$134.70
Purchase #3	$100.40	12.330%	$112.7793	$112.78	$112.80	$112.80
Purchase #4	$230.87	10.533%	$255.1875	$255.19	$255.20	$255.20
Purchase #5	$243.48	6.533%	$259.3865	$259.39	$259.40	$259.40
Purchase #6	$29.61	10.532%	$32.7285	$32.73	$32.75	$32.70
Purchase #7	$70.40	4.365%	$73.473	$73.47	$73.45	$73.50
7 purchase totals =	$844.88		$918.8479	$918.86	$918.90	$918.90