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	$25.54	13.683%	$29.0346	$29.03	$29.05	$29.00
Purchase #2	$37.78	6.519%	$40.2429	$40.24	$40.25	$40.20
Purchase #3	$79.89	13.145%	$90.3915	$90.39	$90.40	$90.40
Purchase #4	$218.27	6.132%	$231.6543	$231.65	$231.65	$231.70
Purchase #5	$76.32	11.527%	$85.1174	$85.12	$85.10	$85.10
Purchase #6	$247.75	10.508%	$273.7836	$273.78	$273.80	$273.80
Purchase #7	$182.40	8.481%	$197.8693	$197.87	$197.85	$197.90
7 purchase totals =	$867.95		$948.0936	$948.08	$948.10	$948.10