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	$40.57	5.584%	$42.8354	$42.84	$42.85	$42.80
Purchase #2	$88.97	11.391%	$99.1046	$99.10	$99.10	$99.10
Purchase #3	$220.77	9.349%	$241.4098	$241.41	$241.40	$241.40
Purchase #4	$237.82	13.423%	$269.7426	$269.74	$269.75	$269.70
Purchase #5	$119.77	12.287%	$134.4861	$134.49	$134.50	$134.50
Purchase #6	$232.36	11.502%	$259.086	$259.09	$259.10	$259.10
Purchase #7	$70.78	8.145%	$76.545	$76.55	$76.55	$76.50
7 purchase totals =	$1,011.04		$1,123.2095	$1,123.22	$1,123.25	$1,123.10