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	$242.37	5.565%	$255.8579	$255.86	$255.85	$255.90
Purchase #2	$79.73	13.622%	$90.5908	$90.59	$90.60	$90.60
Purchase #3	$232.25	10.496%	$256.627	$256.63	$256.65	$256.60
Purchase #4	$192.88	9.716%	$211.6202	$211.62	$211.60	$211.60
Purchase #5	$243.34	6.479%	$259.106	$259.11	$259.10	$259.10
Purchase #6	$148.54	5.846%	$157.2236	$157.22	$157.20	$157.20
Purchase #7	$130.67	12.355%	$146.8143	$146.81	$146.80	$146.80
7 purchase totals =	$1,269.78		$1,377.8398	$1,377.84	$1,377.80	$1,377.80