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	$65.49	5.107%	$68.8346	$68.83	$68.85	$68.80
Purchase #2	$191.94	12.339%	$215.6235	$215.62	$215.60	$215.60
Purchase #3	$21.48	13.492%	$24.3781	$24.38	$24.40	$24.40
Purchase #4	$38.35	11.836%	$42.8891	$42.89	$42.90	$42.90
Purchase #5	$121.78	7.692%	$131.1473	$131.15	$131.15	$131.10
Purchase #6	$141.34	13.102%	$159.8584	$159.86	$159.85	$159.90
Purchase #7	$93.36	8.511%	$101.3059	$101.31	$101.30	$101.30
7 purchase totals =	$673.74		$744.0369	$744.04	$744.05	$744.00