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	$9.74	6.564%	$10.3793	$10.38	$10.40	$10.40
Purchase #2	$166.50	11.190%	$185.1314	$185.13	$185.15	$185.10
Purchase #3	$187.66	9.563%	$205.6059	$205.61	$205.60	$205.60
Purchase #4	$37.97	10.495%	$41.955	$41.96	$41.95	$42.00
Purchase #5	$190.63	11.106%	$211.8014	$211.80	$211.80	$211.80
Purchase #6	$174.34	6.443%	$185.5727	$185.57	$185.55	$185.60
Purchase #7	$66.81	8.859%	$72.7287	$72.73	$72.75	$72.70
7 purchase totals =	$833.65		$913.1744	$913.18	$913.20	$913.20