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	$49.63	13.784%	$56.471	$56.47	$56.45	$56.50
Purchase #2	$97.42	12.328%	$109.4299	$109.43	$109.45	$109.40
Purchase #3	$113.50	3.456%	$117.4226	$117.42	$117.40	$117.40
Purchase #4	$106.67	3.350%	$110.2434	$110.24	$110.25	$110.20
Purchase #5	$44.71	12.359%	$50.2357	$50.24	$50.25	$50.20
Purchase #6	$215.35	12.589%	$242.4604	$242.46	$242.45	$242.50
Purchase #7	$82.87	6.566%	$88.3112	$88.31	$88.30	$88.30
7 purchase totals =	$710.15		$774.5742	$774.57	$774.55	$774.50