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	$211.94	5.142%	$222.838	$222.84	$222.85	$222.80
Purchase #2	$114.93	13.156%	$130.0502	$130.05	$130.05	$130.10
Purchase #3	$38.74	9.865%	$42.5617	$42.56	$42.55	$42.60
Purchase #4	$16.82	9.806%	$18.4694	$18.47	$18.45	$18.50
Purchase #5	$126.60	10.651%	$140.0842	$140.08	$140.10	$140.10
Purchase #6	$239.25	12.655%	$269.5271	$269.53	$269.55	$269.50
Purchase #7	$25.77	12.819%	$29.0735	$29.07	$29.05	$29.10
7 purchase totals =	$774.05		$852.6041	$852.60	$852.60	$852.70