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	$52.63	13.610%	$59.7929	$59.79	$59.80	$59.80
Purchase #2	$26.32	5.665%	$27.811	$27.81	$27.80	$27.80
Purchase #3	$59.75	4.690%	$62.5523	$62.55	$62.55	$62.60
Purchase #4	$77.85	7.586%	$83.7557	$83.76	$83.75	$83.80
Purchase #5	$160.81	12.548%	$180.9884	$180.99	$181.00	$181.00
Purchase #6	$70.47	9.295%	$77.0202	$77.02	$77.00	$77.00
Purchase #7	$114.83	3.534%	$118.8881	$118.89	$118.90	$118.90
7 purchase totals =	$562.66		$610.8086	$610.81	$610.80	$610.90