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	$126.82	3.371%	$131.0951	$131.10	$131.10	$131.10
Purchase #2	$81.37	10.622%	$90.0131	$90.01	$90.00	$90.00
Purchase #3	$77.80	5.591%	$82.1498	$82.15	$82.15	$82.10
Purchase #4	$50.61	7.120%	$54.2134	$54.21	$54.20	$54.20
Purchase #5	$101.89	4.811%	$106.7919	$106.79	$106.80	$106.80
Purchase #6	$98.87	12.368%	$111.0982	$111.10	$111.10	$111.10
Purchase #7	$23.40	6.484%	$24.9173	$24.92	$24.90	$24.90
7 purchase totals =	$560.76		$600.2788	$600.28	$600.25	$600.20