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	$82.94	11.429%	$92.4192	$92.42	$92.40	$92.40
Purchase #2	$206.98	4.204%	$215.6814	$215.68	$215.70	$215.70
Purchase #3	$133.44	4.473%	$139.4088	$139.41	$139.40	$139.40
Purchase #4	$38.26	7.186%	$41.0094	$41.01	$41.00	$41.00
Purchase #5	$93.34	6.780%	$99.6685	$99.67	$99.65	$99.70
Purchase #6	$45.45	12.368%	$51.0713	$51.07	$51.05	$51.10
Purchase #7	$85.62	4.665%	$89.6142	$89.61	$89.60	$89.60
7 purchase totals =	$686.03		$728.8728	$728.87	$728.80	$728.90