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	$76.34	5.314%	$80.3967	$80.40	$80.40	$80.40
Purchase #2	$101.25	11.331%	$112.7226	$112.72	$112.70	$112.70
Purchase #3	$198.43	11.809%	$221.8626	$221.86	$221.85	$221.90
Purchase #4	$90.57	9.324%	$99.0147	$99.01	$99.00	$99.00
Purchase #5	$161.73	10.296%	$178.3817	$178.38	$178.40	$178.40
Purchase #6	$247.29	11.523%	$275.7852	$275.79	$275.80	$275.80
Purchase #7	$154.80	8.805%	$168.4301	$168.43	$168.45	$168.40
7 purchase totals =	$1,030.41		$1,136.5936	$1,136.59	$1,136.60	$1,136.60