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	$123.38	11.801%	$137.9401	$137.94	$137.95	$137.90
Purchase #2	$183.65	5.383%	$193.5359	$193.54	$193.55	$193.50
Purchase #3	$67.73	9.162%	$73.9354	$73.94	$73.95	$73.90
Purchase #4	$60.50	10.106%	$66.6141	$66.61	$66.60	$66.60
Purchase #5	$77.40	3.225%	$79.8962	$79.90	$79.90	$79.90
Purchase #6	$153.38	12.264%	$172.1905	$172.19	$172.20	$172.20
Purchase #7	$104.31	4.537%	$109.0425	$109.04	$109.05	$109.00
7 purchase totals =	$770.35		$833.1547	$833.16	$833.20	$833.00