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	$116.54	12.433%	$131.0294	$131.03	$131.05	$131.00
Purchase #2	$183.64	8.271%	$198.8289	$198.83	$198.85	$198.80
Purchase #3	$195.38	12.822%	$220.4316	$220.43	$220.45	$220.40
Purchase #4	$103.35	5.779%	$109.3226	$109.32	$109.30	$109.30
Purchase #5	$93.93	6.496%	$100.0317	$100.03	$100.05	$100.00
Purchase #6	$199.85	12.720%	$225.2709	$225.27	$225.25	$225.30
Purchase #7	$99.43	9.870%	$109.2437	$109.24	$109.25	$109.20
7 purchase totals =	$992.12		$1,094.1588	$1,094.15	$1,094.20	$1,094.00