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	$46.93	3.119%	$48.3937	$48.39	$48.40	$48.40
Purchase #2	$90.69	7.481%	$97.4745	$97.47	$97.45	$97.50
Purchase #3	$120.75	4.491%	$126.1729	$126.17	$126.15	$126.20
Purchase #4	$215.60	12.722%	$243.0286	$243.03	$243.05	$243.00
Purchase #5	$90.71	10.122%	$99.8917	$99.89	$99.90	$99.90
Purchase #6	$149.96	3.705%	$155.516	$155.52	$155.50	$155.50
Purchase #7	$82.94	6.518%	$88.346	$88.35	$88.35	$88.30
7 purchase totals =	$797.58		$858.8234	$858.82	$858.80	$858.80