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	$12.39	5.220%	$13.0368	$13.04	$13.05	$13.00
Purchase #2	$64.86	7.585%	$69.7796	$69.78	$69.80	$69.80
Purchase #3	$55.41	5.483%	$58.4481	$58.45	$58.45	$58.40
Purchase #4	$173.99	6.470%	$185.2472	$185.25	$185.25	$185.20
Purchase #5	$160.41	13.768%	$182.4952	$182.50	$182.50	$182.50
Purchase #6	$97.85	11.706%	$109.3043	$109.30	$109.30	$109.30
Purchase #7	$106.61	4.481%	$111.3872	$111.39	$111.40	$111.40
7 purchase totals =	$671.52		$729.6984	$729.71	$729.75	$729.60