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	$83.26	5.429%	$87.7802	$87.78	$87.80	$87.80
Purchase #2	$147.50	12.149%	$165.4198	$165.42	$165.40	$165.40
Purchase #3	$98.30	7.454%	$105.6273	$105.63	$105.65	$105.60
Purchase #4	$238.75	13.339%	$270.5969	$270.60	$270.60	$270.60
Purchase #5	$37.73	7.313%	$40.4892	$40.49	$40.50	$40.50
Purchase #6	$182.64	4.359%	$190.6013	$190.60	$190.60	$190.60
Purchase #7	$79.32	8.323%	$85.9218	$85.92	$85.90	$85.90
7 purchase totals =	$867.50		$946.4365	$946.44	$946.45	$946.40