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	$102.27	12.243%	$114.7909	$114.79	$114.80	$114.80
Purchase #2	$143.61	13.859%	$163.5129	$163.51	$163.50	$163.50
Purchase #3	$15.41	8.675%	$16.7468	$16.75	$16.75	$16.70
Purchase #4	$249.38	5.419%	$262.8939	$262.89	$262.90	$262.90
Purchase #5	$42.86	5.453%	$45.1972	$45.20	$45.20	$45.20
Purchase #6	$35.76	11.315%	$39.8062	$39.81	$39.80	$39.80
Purchase #7	$174.92	12.344%	$196.5121	$196.51	$196.50	$196.50
7 purchase totals =	$764.21		$839.4600	$839.46	$839.45	$839.40