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	$104.30	12.222%	$117.0475	$117.05	$117.05	$117.00
Purchase #2	$97.61	5.584%	$103.0605	$103.06	$103.05	$103.10
Purchase #3	$219.53	6.175%	$233.086	$233.09	$233.10	$233.10
Purchase #4	$30.39	5.511%	$32.0648	$32.06	$32.05	$32.10
Purchase #5	$102.62	3.212%	$105.9162	$105.92	$105.90	$105.90
Purchase #6	$94.57	10.341%	$104.3495	$104.35	$104.35	$104.30
Purchase #7	$91.36	11.601%	$101.9587	$101.96	$101.95	$102.00
7 purchase totals =	$740.38		$797.4832	$797.49	$797.45	$797.50