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	$121.83	12.768%	$137.3853	$137.39	$137.40	$137.40
Purchase #2	$156.92	11.814%	$175.4585	$175.46	$175.45	$175.50
Purchase #3	$164.60	6.835%	$175.8504	$175.85	$175.85	$175.90
Purchase #4	$100.68	7.710%	$108.4424	$108.44	$108.45	$108.40
Purchase #5	$237.85	6.154%	$252.4873	$252.49	$252.50	$252.50
Purchase #6	$73.27	13.779%	$83.3659	$83.37	$83.35	$83.40
Purchase #7	$171.28	4.185%	$178.4481	$178.45	$178.45	$178.40
7 purchase totals =	$1,026.43		$1,111.4379	$1,111.45	$1,111.45	$1,111.50