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	$29.92	8.417%	$32.4384	$32.44	$32.45	$32.40
Purchase #2	$224.70	3.224%	$231.9443	$231.94	$231.95	$231.90
Purchase #3	$142.79	12.226%	$160.2475	$160.25	$160.25	$160.20
Purchase #4	$78.39	6.391%	$83.3999	$83.40	$83.40	$83.40
Purchase #5	$202.32	6.503%	$215.4769	$215.48	$215.50	$215.50
Purchase #6	$143.39	5.415%	$151.1546	$151.15	$151.15	$151.20
Purchase #7	$201.53	13.767%	$229.2746	$229.27	$229.25	$229.30
7 purchase totals =	$1,023.04		$1,103.9362	$1,103.93	$1,103.95	$1,103.90