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	$240.28	6.524%	$255.9559	$255.96	$255.95	$256.00
Purchase #2	$236.86	13.693%	$269.2932	$269.29	$269.30	$269.30
Purchase #3	$171.67	11.742%	$191.8275	$191.83	$191.85	$191.80
Purchase #4	$115.41	13.762%	$131.2927	$131.29	$131.30	$131.30
Purchase #5	$79.65	8.349%	$86.3	$86.30	$86.30	$86.30
Purchase #6	$47.38	10.442%	$52.3274	$52.33	$52.35	$52.30
Purchase #7	$186.44	10.266%	$205.5799	$205.58	$205.60	$205.60
7 purchase totals =	$1,077.69		$1,192.5766	$1,192.58	$1,192.65	$1,192.60