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	$231.45	11.638%	$258.3862	$258.39	$258.40	$258.40
Purchase #2	$187.94	4.782%	$196.9273	$196.93	$196.95	$196.90
Purchase #3	$99.97	9.361%	$109.3282	$109.33	$109.35	$109.30
Purchase #4	$180.89	9.277%	$197.6712	$197.67	$197.65	$197.70
Purchase #5	$131.33	11.491%	$146.4211	$146.42	$146.40	$146.40
Purchase #6	$73.45	9.334%	$80.3058	$80.31	$80.30	$80.30
Purchase #7	$185.88	10.548%	$205.4866	$205.49	$205.50	$205.50
7 purchase totals =	$1,090.91		$1,194.5264	$1,194.54	$1,194.55	$1,194.50