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	$250.68	12.333%	$281.5964	$281.60	$281.60	$281.60
Purchase #2	$175.26	12.102%	$196.47	$196.47	$196.45	$196.50
Purchase #3	$209.68	7.510%	$225.427	$225.43	$225.45	$225.40
Purchase #4	$54.35	8.668%	$59.0611	$59.06	$59.05	$59.10
Purchase #5	$8.62	13.310%	$9.7673	$9.77	$9.75	$9.80
Purchase #6	$95.54	4.387%	$99.7313	$99.73	$99.75	$99.70
Purchase #7	$235.83	13.465%	$267.5845	$267.58	$267.60	$267.60
7 purchase totals =	$1,029.96		$1,139.6376	$1,139.64	$1,139.65	$1,139.70