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	$90.49	13.258%	$102.4872	$102.49	$102.50	$102.50
Purchase #2	$247.41	10.683%	$273.8408	$273.84	$273.85	$273.80
Purchase #3	$101.33	7.148%	$108.5731	$108.57	$108.55	$108.60
Purchase #4	$140.82	7.779%	$151.7744	$151.77	$151.75	$151.80
Purchase #5	$109.38	3.732%	$113.4621	$113.46	$113.45	$113.50
Purchase #6	$168.93	13.683%	$192.0447	$192.04	$192.05	$192.00
Purchase #7	$154.52	4.605%	$161.6356	$161.64	$161.65	$161.60
7 purchase totals =	$1,012.88		$1,103.8179	$1,103.81	$1,103.80	$1,103.80