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	$54.92	5.499%	$57.9401	$57.94	$57.95	$57.90
Purchase #2	$105.51	12.130%	$118.3084	$118.31	$118.30	$118.30
Purchase #3	$197.52	13.230%	$223.6519	$223.65	$223.65	$223.70
Purchase #4	$49.85	12.127%	$55.8953	$55.90	$55.90	$55.90
Purchase #5	$133.85	12.842%	$151.039	$151.04	$151.05	$151.00
Purchase #6	$35.33	13.448%	$40.0812	$40.08	$40.10	$40.10
Purchase #7	$18.52	12.783%	$20.8874	$20.89	$20.90	$20.90
7 purchase totals =	$595.50		$667.8033	$667.81	$667.85	$667.80