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	$131.82	5.688%	$139.3179	$139.32	$139.30	$139.30
Purchase #2	$247.36	13.695%	$281.236	$281.24	$281.25	$281.20
Purchase #3	$19.79	10.462%	$21.8604	$21.86	$21.85	$21.90
Purchase #4	$95.28	12.118%	$106.826	$106.83	$106.85	$106.80
Purchase #5	$130.32	11.565%	$145.3915	$145.39	$145.40	$145.40
Purchase #6	$85.31	5.723%	$90.1923	$90.19	$90.20	$90.20
Purchase #7	$116.40	3.690%	$120.6952	$120.70	$120.70	$120.70
7 purchase totals =	$826.28		$905.5193	$905.53	$905.55	$905.50