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	$230.86	12.307%	$259.2719	$259.27	$259.25	$259.30
Purchase #2	$37.73	9.729%	$41.4008	$41.40	$41.40	$41.40
Purchase #3	$196.73	6.570%	$209.6552	$209.66	$209.65	$209.70
Purchase #4	$121.61	12.771%	$137.1408	$137.14	$137.15	$137.10
Purchase #5	$165.74	13.581%	$188.2491	$188.25	$188.25	$188.20
Purchase #6	$114.63	6.480%	$122.058	$122.06	$122.05	$122.10
Purchase #7	$100.27	3.768%	$104.0482	$104.05	$104.05	$104.00
7 purchase totals =	$967.57		$1,061.8240	$1,061.83	$1,061.80	$1,061.80