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	$150.49	10.382%	$166.1139	$166.11	$166.10	$166.10
Purchase #2	$112.77	4.277%	$117.5932	$117.59	$117.60	$117.60
Purchase #3	$36.53	3.484%	$37.8027	$37.80	$37.80	$37.80
Purchase #4	$156.77	7.512%	$168.5466	$168.55	$168.55	$168.50
Purchase #5	$93.38	8.731%	$101.533	$101.53	$101.55	$101.50
Purchase #6	$44.93	7.315%	$48.2166	$48.22	$48.20	$48.20
Purchase #7	$121.92	4.175%	$127.0102	$127.01	$127.00	$127.00
7 purchase totals =	$716.79		$766.8162	$766.81	$766.80	$766.70