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	$45.54	6.713%	$48.5971	$48.60	$48.60	$48.60
Purchase #2	$153.84	13.511%	$174.6253	$174.63	$174.65	$174.60
Purchase #3	$70.93	12.793%	$80.0041	$80.00	$80.00	$80.00
Purchase #4	$196.85	11.196%	$218.8893	$218.89	$218.90	$218.90
Purchase #5	$171.58	5.732%	$181.415	$181.42	$181.40	$181.40
Purchase #6	$61.67	7.378%	$66.22	$66.22	$66.20	$66.20
Purchase #7	$199.83	5.360%	$210.5409	$210.54	$210.55	$210.50
7 purchase totals =	$900.24		$980.2917	$980.30	$980.30	$980.20