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	$161.76	13.466%	$183.5426	$183.54	$183.55	$183.50
Purchase #2	$34.64	4.571%	$36.2234	$36.22	$36.20	$36.20
Purchase #3	$146.70	12.819%	$165.5055	$165.51	$165.50	$165.50
Purchase #4	$102.34	11.864%	$114.4816	$114.48	$114.50	$114.50
Purchase #5	$93.48	7.810%	$100.7808	$100.78	$100.80	$100.80
Purchase #6	$20.26	5.282%	$21.3301	$21.33	$21.35	$21.30
Purchase #7	$150.69	5.211%	$158.5425	$158.54	$158.55	$158.50
7 purchase totals =	$709.87		$780.4065	$780.40	$780.45	$780.30