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	$120.52	8.330%	$130.5593	$130.56	$130.55	$130.60
Purchase #2	$108.89	4.614%	$113.9142	$113.91	$113.90	$113.90
Purchase #3	$161.37	10.365%	$178.096	$178.10	$178.10	$178.10
Purchase #4	$249.28	5.412%	$262.771	$262.77	$262.75	$262.80
Purchase #5	$80.89	11.159%	$89.9165	$89.92	$89.90	$89.90
Purchase #6	$250.36	3.831%	$259.9513	$259.95	$259.95	$260.00
Purchase #7	$40.59	10.326%	$44.7813	$44.78	$44.80	$44.80
7 purchase totals =	$1,011.90		$1,079.9896	$1,079.99	$1,079.95	$1,080.10