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	$247.95	3.238%	$255.9786	$255.98	$256.00	$256.00
Purchase #2	$100.89	13.373%	$114.382	$114.38	$114.40	$114.40
Purchase #3	$156.78	4.807%	$164.3164	$164.32	$164.30	$164.30
Purchase #4	$104.76	10.628%	$115.8939	$115.89	$115.90	$115.90
Purchase #5	$123.39	3.825%	$128.1097	$128.11	$128.10	$128.10
Purchase #6	$89.55	13.280%	$101.4422	$101.44	$101.45	$101.40
Purchase #7	$157.40	11.175%	$174.9895	$174.99	$175.00	$175.00
7 purchase totals =	$980.72		$1,055.1123	$1,055.11	$1,055.15	$1,055.10