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	$228.89	13.459%	$259.6963	$259.70	$259.70	$259.70
Purchase #2	$54.56	8.436%	$59.1627	$59.16	$59.15	$59.20
Purchase #3	$80.46	3.671%	$83.4137	$83.41	$83.40	$83.40
Purchase #4	$141.87	7.312%	$152.2435	$152.24	$152.25	$152.20
Purchase #5	$106.46	5.238%	$112.0364	$112.04	$112.05	$112.00
Purchase #6	$34.47	13.513%	$39.1279	$39.13	$39.15	$39.10
Purchase #7	$5.67	6.333%	$6.0291	$6.03	$6.05	$6.00
7 purchase totals =	$652.38		$711.7096	$711.71	$711.75	$711.60