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	$203.60	12.852%	$229.7667	$229.77	$229.75	$229.80
Purchase #2	$80.84	5.397%	$85.2029	$85.20	$85.20	$85.20
Purchase #3	$241.79	11.196%	$268.8608	$268.86	$268.85	$268.90
Purchase #4	$29.47	13.764%	$33.5263	$33.53	$33.55	$33.50
Purchase #5	$107.72	12.272%	$120.9394	$120.94	$120.95	$120.90
Purchase #6	$178.70	7.656%	$192.3813	$192.38	$192.40	$192.40
Purchase #7	$160.90	7.229%	$172.5315	$172.53	$172.55	$172.50
7 purchase totals =	$1,003.02		$1,103.2089	$1,103.21	$1,103.25	$1,103.20