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	$144.41	10.654%	$159.7954	$159.80	$159.80	$159.80
Purchase #2	$153.79	5.761%	$162.6498	$162.65	$162.65	$162.60
Purchase #3	$160.34	8.426%	$173.8502	$173.85	$173.85	$173.90
Purchase #4	$174.41	8.649%	$189.4947	$189.49	$189.50	$189.50
Purchase #5	$233.74	4.711%	$244.7515	$244.75	$244.75	$244.80
Purchase #6	$68.30	6.215%	$72.5448	$72.54	$72.55	$72.50
Purchase #7	$129.33	5.258%	$136.1302	$136.13	$136.15	$136.10
7 purchase totals =	$1,064.32		$1,139.2166	$1,139.21	$1,139.25	$1,139.20