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	$79.84	4.506%	$83.4376	$83.44	$83.45	$83.40
Purchase #2	$247.66	13.395%	$280.8341	$280.83	$280.85	$280.80
Purchase #3	$92.29	8.868%	$100.4743	$100.47	$100.45	$100.50
Purchase #4	$61.48	8.103%	$66.4617	$66.46	$66.45	$66.50
Purchase #5	$94.91	4.167%	$98.8649	$98.86	$98.85	$98.90
Purchase #6	$216.81	13.502%	$246.0837	$246.08	$246.10	$246.10
Purchase #7	$41.34	11.339%	$46.0275	$46.03	$46.05	$46.00
7 purchase totals =	$834.33		$922.1838	$922.17	$922.20	$922.20