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	$120.90	8.612%	$131.3119	$131.31	$131.30	$131.30
Purchase #2	$76.79	12.565%	$86.4387	$86.44	$86.45	$86.40
Purchase #3	$238.49	11.316%	$265.4775	$265.48	$265.50	$265.50
Purchase #4	$94.94	10.449%	$104.8603	$104.86	$104.85	$104.90
Purchase #5	$47.99	4.236%	$50.0229	$50.02	$50.00	$50.00
Purchase #6	$45.39	6.362%	$48.2777	$48.28	$48.30	$48.30
Purchase #7	$227.43	8.793%	$247.4279	$247.43	$247.45	$247.40
7 purchase totals =	$851.93		$933.8169	$933.82	$933.85	$933.80