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	$98.93	3.759%	$102.6488	$102.65	$102.65	$102.60
Purchase #2	$92.60	8.282%	$100.2691	$100.27	$100.25	$100.30
Purchase #3	$40.27	3.478%	$41.6706	$41.67	$41.65	$41.70
Purchase #4	$105.85	13.521%	$120.162	$120.16	$120.15	$120.20
Purchase #5	$145.93	12.852%	$164.6849	$164.68	$164.70	$164.70
Purchase #6	$241.94	13.601%	$274.8463	$274.85	$274.85	$274.80
Purchase #7	$73.86	6.460%	$78.6314	$78.63	$78.65	$78.60
7 purchase totals =	$799.38		$882.9131	$882.91	$882.90	$882.90