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	$158.51	12.620%	$178.514	$178.51	$178.50	$178.50
Purchase #2	$102.25	8.326%	$110.7633	$110.76	$110.75	$110.80
Purchase #3	$113.48	5.205%	$119.3866	$119.39	$119.40	$119.40
Purchase #4	$87.76	13.349%	$99.4751	$99.48	$99.50	$99.50
Purchase #5	$130.91	6.526%	$139.4532	$139.45	$139.45	$139.50
Purchase #6	$222.54	10.387%	$245.6552	$245.66	$245.65	$245.70
Purchase #7	$44.86	7.728%	$48.3268	$48.33	$48.35	$48.30
7 purchase totals =	$860.31		$941.5742	$941.58	$941.60	$941.70