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	$115.83	3.518%	$119.9049	$119.90	$119.90	$119.90
Purchase #2	$114.42	6.821%	$122.2246	$122.22	$122.20	$122.20
Purchase #3	$36.28	12.133%	$40.6819	$40.68	$40.70	$40.70
Purchase #4	$98.80	12.353%	$111.0048	$111.00	$111.00	$111.00
Purchase #5	$189.68	3.570%	$196.4516	$196.45	$196.45	$196.50
Purchase #6	$128.34	12.503%	$144.3864	$144.39	$144.40	$144.40
Purchase #7	$26.84	4.518%	$28.0526	$28.05	$28.05	$28.10
7 purchase totals =	$710.19		$762.7068	$762.69	$762.70	$762.80