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	$109.90	6.721%	$117.2864	$117.29	$117.30	$117.30
Purchase #2	$144.63	5.103%	$152.0105	$152.01	$152.00	$152.00
Purchase #3	$12.56	7.223%	$13.4672	$13.47	$13.45	$13.50
Purchase #4	$93.59	13.516%	$106.2396	$106.24	$106.25	$106.20
Purchase #5	$94.67	10.169%	$104.297	$104.30	$104.30	$104.30
Purchase #6	$30.40	10.146%	$33.4844	$33.48	$33.50	$33.50
Purchase #7	$54.45	5.418%	$57.4001	$57.40	$57.40	$57.40
7 purchase totals =	$540.20		$584.1852	$584.19	$584.20	$584.20