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	$215.90	7.378%	$231.8291	$231.83	$231.85	$231.80
Purchase #2	$113.86	4.113%	$118.5431	$118.54	$118.55	$118.50
Purchase #3	$149.53	12.512%	$168.2392	$168.24	$168.25	$168.20
Purchase #4	$154.61	6.636%	$164.8699	$164.87	$164.85	$164.90
Purchase #5	$53.63	10.416%	$59.2161	$59.22	$59.20	$59.20
Purchase #6	$113.49	5.600%	$119.8454	$119.85	$119.85	$119.80
Purchase #7	$73.34	7.721%	$79.0026	$79.00	$79.00	$79.00
7 purchase totals =	$874.36		$941.5454	$941.55	$941.55	$941.40