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	$70.57	6.443%	$75.1168	$75.12	$75.10	$75.10
Purchase #2	$235.89	4.150%	$245.6794	$245.68	$245.70	$245.70
Purchase #3	$138.91	9.257%	$151.7689	$151.77	$151.75	$151.80
Purchase #4	$85.79	5.688%	$90.6697	$90.67	$90.65	$90.70
Purchase #5	$35.94	12.335%	$40.3732	$40.37	$40.35	$40.40
Purchase #6	$235.64	8.468%	$255.594	$255.59	$255.60	$255.60
Purchase #7	$200.59	6.343%	$213.3134	$213.31	$213.30	$213.30
7 purchase totals =	$1,003.33		$1,072.5154	$1,072.51	$1,072.45	$1,072.60