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	$66.91	6.380%	$71.1789	$71.18	$71.20	$71.20
Purchase #2	$132.34	7.658%	$142.4746	$142.47	$142.45	$142.50
Purchase #3	$209.88	7.434%	$225.4825	$225.48	$225.50	$225.50
Purchase #4	$203.69	7.563%	$219.0951	$219.10	$219.10	$219.10
Purchase #5	$193.70	12.678%	$218.2573	$218.26	$218.25	$218.30
Purchase #6	$158.63	7.798%	$171	$171.00	$171.00	$171.00
Purchase #7	$22.45	7.404%	$24.1122	$24.11	$24.10	$24.10
7 purchase totals =	$987.60		$1,071.6006	$1,071.60	$1,071.60	$1,071.70