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	$89.88	12.827%	$101.4089	$101.41	$101.40	$101.40
Purchase #2	$124.71	5.513%	$131.5853	$131.59	$131.60	$131.60
Purchase #3	$91.43	13.694%	$103.9504	$103.95	$103.95	$104.00
Purchase #4	$80.49	7.357%	$86.4116	$86.41	$86.40	$86.40
Purchase #5	$35.81	10.561%	$39.5919	$39.59	$39.60	$39.60
Purchase #6	$219.31	10.447%	$242.2213	$242.22	$242.20	$242.20
Purchase #7	$59.53	10.658%	$65.8747	$65.87	$65.85	$65.90
7 purchase totals =	$701.16		$771.0441	$771.04	$771.00	$771.10