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	$48.83	11.366%	$54.38	$54.38	$54.40	$54.40
Purchase #2	$129.59	13.350%	$146.8903	$146.89	$146.90	$146.90
Purchase #3	$75.76	5.473%	$79.9063	$79.91	$79.90	$79.90
Purchase #4	$24.29	13.345%	$27.5315	$27.53	$27.55	$27.50
Purchase #5	$176.25	9.392%	$192.8034	$192.80	$192.80	$192.80
Purchase #6	$125.98	13.421%	$142.8878	$142.89	$142.90	$142.90
Purchase #7	$233.90	5.243%	$246.1634	$246.16	$246.15	$246.20
7 purchase totals =	$814.60		$890.5627	$890.56	$890.60	$890.60