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	$100.91	8.553%	$109.5408	$109.54	$109.55	$109.50
Purchase #2	$218.76	12.693%	$246.5272	$246.53	$246.55	$246.50
Purchase #3	$112.78	13.729%	$128.2636	$128.26	$128.25	$128.30
Purchase #4	$118.89	7.287%	$127.5535	$127.55	$127.55	$127.60
Purchase #5	$52.47	12.458%	$59.0067	$59.01	$59.00	$59.00
Purchase #6	$224.63	7.163%	$240.7202	$240.72	$240.70	$240.70
Purchase #7	$209.90	7.204%	$225.0212	$225.02	$225.00	$225.00
7 purchase totals =	$1,038.34		$1,136.6332	$1,136.63	$1,136.60	$1,136.60