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	$52.84	4.507%	$55.2215	$55.22	$55.20	$55.20
Purchase #2	$34.61	7.409%	$37.1743	$37.17	$37.15	$37.20
Purchase #3	$96.95	7.762%	$104.4753	$104.48	$104.50	$104.50
Purchase #4	$62.64	6.798%	$66.8983	$66.90	$66.90	$66.90
Purchase #5	$102.89	6.271%	$109.3422	$109.34	$109.35	$109.30
Purchase #6	$186.93	7.373%	$200.7123	$200.71	$200.70	$200.70
Purchase #7	$43.96	12.545%	$49.4748	$49.47	$49.45	$49.50
7 purchase totals =	$580.82		$623.2987	$623.29	$623.25	$623.30