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	$92.55	12.176%	$103.8189	$103.82	$103.80	$103.80
Purchase #2	$174.77	10.323%	$192.8115	$192.81	$192.80	$192.80
Purchase #3	$55.72	10.435%	$61.5344	$61.53	$61.55	$61.50
Purchase #4	$162.68	11.307%	$181.0742	$181.07	$181.05	$181.10
Purchase #5	$6.80	4.338%	$7.095	$7.10	$7.10	$7.10
Purchase #6	$204.90	13.104%	$231.7501	$231.75	$231.75	$231.80
Purchase #7	$42.96	7.312%	$46.1012	$46.10	$46.10	$46.10
7 purchase totals =	$740.38		$824.1853	$824.18	$824.15	$824.20