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	$243.35	6.676%	$259.596	$259.60	$259.60	$259.60
Purchase #2	$79.70	7.265%	$85.4902	$85.49	$85.50	$85.50
Purchase #3	$184.58	8.660%	$200.5646	$200.56	$200.55	$200.60
Purchase #4	$218.82	12.247%	$245.6189	$245.62	$245.60	$245.60
Purchase #5	$152.55	13.736%	$173.5043	$173.50	$173.50	$173.50
Purchase #6	$131.48	6.673%	$140.2537	$140.25	$140.25	$140.30
Purchase #7	$122.53	11.703%	$136.8697	$136.87	$136.85	$136.90
7 purchase totals =	$1,133.01		$1,241.8974	$1,241.89	$1,241.85	$1,242.00