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	$17.63	5.116%	$18.532	$18.53	$18.55	$18.50
Purchase #2	$12.54	6.205%	$13.3181	$13.32	$13.30	$13.30
Purchase #3	$243.63	7.497%	$261.8949	$261.89	$261.90	$261.90
Purchase #4	$68.97	4.146%	$71.8295	$71.83	$71.85	$71.80
Purchase #5	$123.82	5.734%	$130.9198	$130.92	$130.90	$130.90
Purchase #6	$247.54	13.579%	$281.1535	$281.15	$281.15	$281.20
Purchase #7	$95.74	7.152%	$102.5873	$102.59	$102.60	$102.60
7 purchase totals =	$809.87		$880.2351	$880.23	$880.25	$880.20