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	$123.40	6.359%	$131.247	$131.25	$131.25	$131.20
Purchase #2	$93.68	12.136%	$105.049	$105.05	$105.05	$105.00
Purchase #3	$5.80	11.106%	$6.4441	$6.44	$6.45	$6.40
Purchase #4	$126.42	12.444%	$142.1517	$142.15	$142.15	$142.20
Purchase #5	$90.59	4.561%	$94.7218	$94.72	$94.70	$94.70
Purchase #6	$71.67	8.499%	$77.7612	$77.76	$77.75	$77.80
Purchase #7	$78.79	11.548%	$87.8887	$87.89	$87.90	$87.90
7 purchase totals =	$590.35		$645.2635	$645.26	$645.25	$645.20