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	$150.39	13.730%	$171.0385	$171.04	$171.05	$171.00
Purchase #2	$110.78	11.277%	$123.2727	$123.27	$123.25	$123.30
Purchase #3	$45.74	8.370%	$49.5684	$49.57	$49.55	$49.60
Purchase #4	$41.81	13.270%	$47.3582	$47.36	$47.35	$47.40
Purchase #5	$82.89	7.857%	$89.4027	$89.40	$89.40	$89.40
Purchase #6	$76.42	11.313%	$85.0654	$85.07	$85.05	$85.10
Purchase #7	$180.70	5.253%	$190.1922	$190.19	$190.20	$190.20
7 purchase totals =	$688.73		$755.8981	$755.90	$755.85	$756.00