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	$72.45	9.656%	$79.4458	$79.45	$79.45	$79.40
Purchase #2	$104.35	4.712%	$109.267	$109.27	$109.25	$109.30
Purchase #3	$248.78	11.754%	$278.0216	$278.02	$278.00	$278.00
Purchase #4	$196.66	8.675%	$213.7203	$213.72	$213.70	$213.70
Purchase #5	$149.61	3.709%	$155.159	$155.16	$155.15	$155.20
Purchase #6	$76.72	3.564%	$79.4543	$79.45	$79.45	$79.50
Purchase #7	$219.26	7.550%	$235.8141	$235.81	$235.80	$235.80
7 purchase totals =	$1,067.83		$1,150.8821	$1,150.88	$1,150.80	$1,150.90