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	$96.71	6.129%	$102.6374	$102.64	$102.65	$102.60
Purchase #2	$163.27	5.446%	$172.1617	$172.16	$172.15	$172.20
Purchase #3	$89.30	3.615%	$92.5282	$92.53	$92.55	$92.50
Purchase #4	$121.91	7.620%	$131.1995	$131.20	$131.20	$131.20
Purchase #5	$115.76	8.426%	$125.5139	$125.51	$125.50	$125.50
Purchase #6	$93.45	6.288%	$99.3261	$99.33	$99.35	$99.30
Purchase #7	$132.33	3.613%	$137.1111	$137.11	$137.10	$137.10
7 purchase totals =	$812.73		$860.4779	$860.48	$860.50	$860.40