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	$241.66	6.139%	$256.4955	$256.50	$256.50	$256.50
Purchase #2	$190.27	3.144%	$196.2521	$196.25	$196.25	$196.30
Purchase #3	$123.34	4.440%	$128.8163	$128.82	$128.80	$128.80
Purchase #4	$245.69	7.147%	$263.2495	$263.25	$263.25	$263.20
Purchase #5	$80.36	13.535%	$91.2367	$91.24	$91.25	$91.20
Purchase #6	$116.25	11.286%	$129.37	$129.37	$129.35	$129.40
Purchase #7	$220.37	3.751%	$228.6361	$228.64	$228.65	$228.60
7 purchase totals =	$1,217.94		$1,294.0562	$1,294.07	$1,294.05	$1,294.00