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	$170.67	7.232%	$183.0129	$183.01	$183.00	$183.00
Purchase #2	$210.83	8.775%	$229.3303	$229.33	$229.35	$229.30
Purchase #3	$150.61	9.560%	$165.0083	$165.01	$165.00	$165.00
Purchase #4	$71.72	8.213%	$77.6104	$77.61	$77.60	$77.60
Purchase #5	$148.52	10.512%	$164.1324	$164.13	$164.15	$164.10
Purchase #6	$222.97	12.335%	$250.4733	$250.47	$250.45	$250.50
Purchase #7	$165.61	13.419%	$187.8332	$187.83	$187.85	$187.80
7 purchase totals =	$1,140.93		$1,257.4008	$1,257.39	$1,257.40	$1,257.30