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	$24.26	12.404%	$27.2692	$27.27	$27.25	$27.30
Purchase #2	$64.64	9.662%	$70.8855	$70.89	$70.90	$70.90
Purchase #3	$70.69	11.643%	$78.9204	$78.92	$78.90	$78.90
Purchase #4	$96.83	7.188%	$103.7901	$103.79	$103.80	$103.80
Purchase #5	$102.72	10.604%	$113.6124	$113.61	$113.60	$113.60
Purchase #6	$92.85	11.146%	$103.1991	$103.20	$103.20	$103.20
Purchase #7	$218.84	5.473%	$230.8171	$230.82	$230.80	$230.80
7 purchase totals =	$670.83		$728.4938	$728.50	$728.45	$728.50