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	$6.54	8.601%	$7.1025	$7.10	$7.10	$7.10
Purchase #2	$77.30	4.599%	$80.855	$80.86	$80.85	$80.90
Purchase #3	$238.37	10.308%	$262.9412	$262.94	$262.95	$262.90
Purchase #4	$150.95	11.176%	$167.8202	$167.82	$167.80	$167.80
Purchase #5	$93.44	7.233%	$100.1985	$100.20	$100.20	$100.20
Purchase #6	$62.75	13.554%	$71.2551	$71.26	$71.25	$71.30
Purchase #7	$205.99	11.531%	$229.7427	$229.74	$229.75	$229.70
7 purchase totals =	$835.34		$919.9152	$919.92	$919.90	$919.90