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	$30.61	7.518%	$32.9113	$32.91	$32.90	$32.90
Purchase #2	$247.76	13.685%	$281.666	$281.67	$281.65	$281.70
Purchase #3	$22.35	11.405%	$24.899	$24.90	$24.90	$24.90
Purchase #4	$35.93	12.215%	$40.3188	$40.32	$40.30	$40.30
Purchase #5	$51.34	9.724%	$56.3323	$56.33	$56.35	$56.30
Purchase #6	$169.69	12.473%	$190.8554	$190.86	$190.85	$190.90
Purchase #7	$84.27	7.390%	$90.4976	$90.50	$90.50	$90.50
7 purchase totals =	$641.95		$717.4804	$717.49	$717.45	$717.50