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	$29.44	9.598%	$32.2657	$32.27	$32.25	$32.30
Purchase #2	$143.70	4.464%	$150.1148	$150.11	$150.10	$150.10
Purchase #3	$123.50	12.870%	$139.3945	$139.39	$139.40	$139.40
Purchase #4	$98.84	7.822%	$106.5713	$106.57	$106.55	$106.60
Purchase #5	$133.39	7.143%	$142.918	$142.92	$142.90	$142.90
Purchase #6	$206.88	9.509%	$226.5522	$226.55	$226.55	$226.60
Purchase #7	$33.35	11.260%	$37.1052	$37.11	$37.10	$37.10
7 purchase totals =	$769.10		$834.9217	$834.92	$834.85	$835.00