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	$111.65	7.473%	$119.9936	$119.99	$120.00	$120.00
Purchase #2	$39.39	6.624%	$41.9992	$42.00	$42.00	$42.00
Purchase #3	$73.99	3.378%	$76.4894	$76.49	$76.50	$76.50
Purchase #4	$250.56	12.279%	$281.3263	$281.33	$281.35	$281.30
Purchase #5	$203.89	7.694%	$219.5773	$219.58	$219.60	$219.60
Purchase #6	$98.69	7.233%	$105.8282	$105.83	$105.85	$105.80
Purchase #7	$181.34	8.461%	$196.6832	$196.68	$196.70	$196.70
7 purchase totals =	$959.51		$1,041.8972	$1,041.90	$1,042.00	$1,041.90