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	$17.41	10.736%	$19.2791	$19.28	$19.30	$19.30
Purchase #2	$216.52	8.758%	$235.4828	$235.48	$235.50	$235.50
Purchase #3	$79.79	12.241%	$89.5571	$89.56	$89.55	$89.60
Purchase #4	$14.38	12.836%	$16.2258	$16.23	$16.25	$16.20
Purchase #5	$19.54	12.192%	$21.9223	$21.92	$21.90	$21.90
Purchase #6	$56.77	10.378%	$62.6616	$62.66	$62.65	$62.70
Purchase #7	$65.63	10.741%	$72.6793	$72.68	$72.70	$72.70
7 purchase totals =	$470.04		$517.8080	$517.81	$517.85	$517.90