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	$71.53	12.583%	$80.5306	$80.53	$80.55	$80.50
Purchase #2	$33.60	8.631%	$36.5	$36.50	$36.50	$36.50
Purchase #3	$82.31	10.139%	$90.6554	$90.66	$90.65	$90.70
Purchase #4	$130.60	7.175%	$139.9706	$139.97	$139.95	$140.00
Purchase #5	$151.91	10.246%	$167.4747	$167.47	$167.45	$167.50
Purchase #6	$192.43	13.375%	$218.1675	$218.17	$218.15	$218.20
Purchase #7	$240.63	9.498%	$263.485	$263.49	$263.50	$263.50
7 purchase totals =	$903.01		$996.7838	$996.79	$996.75	$996.90