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	$54.82	12.359%	$61.5952	$61.60	$61.60	$61.60
Purchase #2	$169.81	12.140%	$190.4249	$190.42	$190.40	$190.40
Purchase #3	$45.78	3.702%	$47.4748	$47.47	$47.45	$47.50
Purchase #4	$247.86	12.751%	$279.4646	$279.46	$279.45	$279.50
Purchase #5	$188.27	12.459%	$211.7266	$211.73	$211.75	$211.70
Purchase #6	$222.56	6.620%	$237.2935	$237.29	$237.30	$237.30
Purchase #7	$166.67	6.824%	$178.0436	$178.04	$178.05	$178.00
7 purchase totals =	$1,095.77		$1,206.0232	$1,206.01	$1,206.00	$1,206.00