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	$40.61	3.543%	$42.0488	$42.05	$42.05	$42.00
Purchase #2	$152.32	6.706%	$162.5346	$162.53	$162.55	$162.50
Purchase #3	$71.30	7.581%	$76.7053	$76.71	$76.70	$76.70
Purchase #4	$188.73	3.578%	$195.4828	$195.48	$195.50	$195.50
Purchase #5	$34.52	8.856%	$37.5771	$37.58	$37.60	$37.60
Purchase #6	$196.41	4.599%	$205.4429	$205.44	$205.45	$205.40
Purchase #7	$136.40	10.456%	$150.662	$150.66	$150.65	$150.70
7 purchase totals =	$820.29		$870.4535	$870.45	$870.50	$870.40