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	$171.68	4.202%	$178.894	$178.89	$178.90	$178.90
Purchase #2	$136.70	11.641%	$152.6132	$152.61	$152.60	$152.60
Purchase #3	$110.66	5.250%	$116.4697	$116.47	$116.45	$116.50
Purchase #4	$164.27	6.635%	$175.1693	$175.17	$175.15	$175.20
Purchase #5	$232.72	10.695%	$257.6094	$257.61	$257.60	$257.60
Purchase #6	$64.67	12.336%	$72.6477	$72.65	$72.65	$72.60
Purchase #7	$80.61	11.821%	$90.1389	$90.14	$90.15	$90.10
7 purchase totals =	$961.31		$1,043.5422	$1,043.54	$1,043.50	$1,043.50