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	$17.32	8.116%	$18.7257	$18.73	$18.75	$18.70
Purchase #2	$27.77	12.339%	$31.1965	$31.20	$31.20	$31.20
Purchase #3	$89.54	5.389%	$94.3653	$94.37	$94.35	$94.40
Purchase #4	$158.30	6.835%	$169.1198	$169.12	$169.10	$169.10
Purchase #5	$114.75	10.807%	$127.151	$127.15	$127.15	$127.20
Purchase #6	$89.53	10.214%	$98.6746	$98.67	$98.65	$98.70
Purchase #7	$13.54	13.399%	$15.3542	$15.35	$15.35	$15.40
7 purchase totals =	$510.75		$554.5871	$554.59	$554.55	$554.70