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	$245.98	11.706%	$274.7744	$274.77	$274.75	$274.80
Purchase #2	$106.34	4.682%	$111.3188	$111.32	$111.30	$111.30
Purchase #3	$205.52	13.404%	$233.0679	$233.07	$233.05	$233.10
Purchase #4	$126.90	11.460%	$141.4427	$141.44	$141.45	$141.40
Purchase #5	$121.65	3.248%	$125.6012	$125.60	$125.60	$125.60
Purchase #6	$15.69	6.862%	$16.7666	$16.77	$16.75	$16.80
Purchase #7	$191.98	9.124%	$209.4963	$209.50	$209.50	$209.50
7 purchase totals =	$1,014.06		$1,112.4679	$1,112.47	$1,112.40	$1,112.50