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	$38.32	10.822%	$42.467	$42.47	$42.45	$42.50
Purchase #2	$186.77	11.557%	$208.355	$208.36	$208.35	$208.40
Purchase #3	$77.68	11.835%	$86.8734	$86.87	$86.85	$86.90
Purchase #4	$89.88	9.609%	$98.5166	$98.52	$98.50	$98.50
Purchase #5	$138.78	4.134%	$144.5172	$144.52	$144.50	$144.50
Purchase #6	$106.56	10.817%	$118.0866	$118.09	$118.10	$118.10
Purchase #7	$100.69	8.367%	$109.1147	$109.11	$109.10	$109.10
7 purchase totals =	$738.68		$807.9305	$807.94	$807.85	$808.00