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	$78.60	8.803%	$85.5192	$85.52	$85.50	$85.50
Purchase #2	$207.67	10.461%	$229.3944	$229.39	$229.40	$229.40
Purchase #3	$59.28	6.693%	$63.2476	$63.25	$63.25	$63.20
Purchase #4	$55.74	3.133%	$57.4863	$57.49	$57.50	$57.50
Purchase #5	$137.52	3.122%	$141.8134	$141.81	$141.80	$141.80
Purchase #6	$212.63	4.691%	$222.6045	$222.60	$222.60	$222.60
Purchase #7	$73.46	4.532%	$76.7892	$76.79	$76.80	$76.80
7 purchase totals =	$824.90		$876.8546	$876.85	$876.85	$876.80