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	$84.38	6.795%	$90.1136	$90.11	$90.10	$90.10
Purchase #2	$5.82	13.107%	$6.5828	$6.58	$6.60	$6.60
Purchase #3	$160.26	12.823%	$180.8101	$180.81	$180.80	$180.80
Purchase #4	$62.27	6.365%	$66.2335	$66.23	$66.25	$66.20
Purchase #5	$213.54	4.226%	$222.5642	$222.56	$222.55	$222.60
Purchase #6	$31.75	3.556%	$32.879	$32.88	$32.90	$32.90
Purchase #7	$84.95	11.472%	$94.6955	$94.70	$94.70	$94.70
7 purchase totals =	$642.97		$693.8787	$693.87	$693.90	$693.90