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	$44.33	10.176%	$48.841	$48.84	$48.85	$48.80
Purchase #2	$162.71	10.581%	$179.9263	$179.93	$179.95	$179.90
Purchase #3	$115.83	6.688%	$123.5767	$123.58	$123.60	$123.60
Purchase #4	$121.84	9.175%	$133.0188	$133.02	$133.00	$133.00
Purchase #5	$176.89	7.874%	$190.8183	$190.82	$190.80	$190.80
Purchase #6	$106.90	3.831%	$110.9953	$111.00	$111.00	$111.00
Purchase #7	$50.88	8.507%	$55.2084	$55.21	$55.20	$55.20
7 purchase totals =	$779.38		$842.3848	$842.40	$842.40	$842.30