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	$148.73	13.211%	$168.3787	$168.38	$168.40	$168.40
Purchase #2	$28.64	13.495%	$32.505	$32.51	$32.50	$32.50
Purchase #3	$134.85	11.580%	$150.4656	$150.47	$150.45	$150.50
Purchase #4	$221.73	12.837%	$250.1935	$250.19	$250.20	$250.20
Purchase #5	$211.77	6.312%	$225.1369	$225.14	$225.15	$225.10
Purchase #6	$70.37	6.343%	$74.8336	$74.83	$74.85	$74.80
Purchase #7	$15.77	13.737%	$17.9363	$17.94	$17.95	$17.90
7 purchase totals =	$831.86		$919.4496	$919.46	$919.50	$919.40