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	$144.40	12.372%	$162.2652	$162.27	$162.25	$162.30
Purchase #2	$249.46	4.381%	$260.3888	$260.39	$260.40	$260.40
Purchase #3	$72.82	8.276%	$78.8466	$78.85	$78.85	$78.80
Purchase #4	$63.59	3.783%	$65.9956	$66.00	$66.00	$66.00
Purchase #5	$89.73	11.426%	$99.9825	$99.98	$100.00	$100.00
Purchase #6	$200.95	10.730%	$222.5119	$222.51	$222.50	$222.50
Purchase #7	$86.36	7.483%	$92.8223	$92.82	$92.80	$92.80
7 purchase totals =	$907.31		$982.8129	$982.82	$982.80	$982.80