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	$42.37	8.271%	$45.8744	$45.87	$45.85	$45.90
Purchase #2	$55.85	10.294%	$61.5992	$61.60	$61.60	$61.60
Purchase #3	$113.72	5.361%	$119.8165	$119.82	$119.80	$119.80
Purchase #4	$38.95	10.825%	$43.1663	$43.17	$43.15	$43.20
Purchase #5	$213.60	10.796%	$236.6603	$236.66	$236.65	$236.70
Purchase #6	$27.66	12.745%	$31.1853	$31.19	$31.20	$31.20
Purchase #7	$11.25	5.136%	$11.8278	$11.83	$11.85	$11.80
7 purchase totals =	$503.40		$550.1298	$550.14	$550.10	$550.20