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	$40.73	4.232%	$42.4537	$42.45	$42.45	$42.50
Purchase #2	$122.43	13.605%	$139.0866	$139.09	$139.10	$139.10
Purchase #3	$229.35	9.794%	$251.8125	$251.81	$251.80	$251.80
Purchase #4	$33.87	11.373%	$37.722	$37.72	$37.70	$37.70
Purchase #5	$136.31	4.231%	$142.0773	$142.08	$142.10	$142.10
Purchase #6	$243.84	4.162%	$253.9886	$253.99	$254.00	$254.00
Purchase #7	$208.27	9.152%	$227.3309	$227.33	$227.35	$227.30
7 purchase totals =	$1,014.80		$1,094.4716	$1,094.47	$1,094.50	$1,094.50