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	$150.63	12.155%	$168.9391	$168.94	$168.95	$168.90
Purchase #2	$93.45	6.603%	$99.6205	$99.62	$99.60	$99.60
Purchase #3	$177.66	3.770%	$184.3578	$184.36	$184.35	$184.40
Purchase #4	$157.71	13.811%	$179.4913	$179.49	$179.50	$179.50
Purchase #5	$51.92	4.312%	$54.1588	$54.16	$54.15	$54.20
Purchase #6	$201.98	6.275%	$214.6542	$214.65	$214.65	$214.70
Purchase #7	$76.54	11.488%	$85.3329	$85.33	$85.35	$85.30
7 purchase totals =	$909.89		$986.5546	$986.55	$986.55	$986.60