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	$100.69	6.820%	$107.5571	$107.56	$107.55	$107.60
Purchase #2	$96.65	7.825%	$104.2129	$104.21	$104.20	$104.20
Purchase #3	$54.80	6.116%	$58.1516	$58.15	$58.15	$58.20
Purchase #4	$100.39	5.731%	$106.1434	$106.14	$106.15	$106.10
Purchase #5	$76.89	11.556%	$85.7754	$85.78	$85.80	$85.80
Purchase #6	$20.39	3.521%	$21.1079	$21.11	$21.10	$21.10
Purchase #7	$54.71	8.104%	$59.1437	$59.14	$59.15	$59.10
7 purchase totals =	$504.52		$542.0920	$542.09	$542.10	$542.10