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	$130.74	10.503%	$144.4716	$144.47	$144.45	$144.50
Purchase #2	$205.69	11.455%	$229.2518	$229.25	$229.25	$229.30
Purchase #3	$18.48	13.131%	$20.9066	$20.91	$20.90	$20.90
Purchase #4	$101.96	5.788%	$107.8614	$107.86	$107.85	$107.90
Purchase #5	$27.78	13.431%	$31.5111	$31.51	$31.50	$31.50
Purchase #6	$187.80	11.389%	$209.1885	$209.19	$209.20	$209.20
Purchase #7	$88.97	8.298%	$96.3527	$96.35	$96.35	$96.40
7 purchase totals =	$761.42		$839.5437	$839.54	$839.50	$839.70