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	$127.95	8.648%	$139.0151	$139.02	$139.00	$139.00
Purchase #2	$21.72	11.764%	$24.2751	$24.28	$24.30	$24.30
Purchase #3	$144.98	5.340%	$152.7219	$152.72	$152.70	$152.70
Purchase #4	$18.38	11.487%	$20.4913	$20.49	$20.50	$20.50
Purchase #5	$100.46	6.425%	$106.9146	$106.91	$106.90	$106.90
Purchase #6	$75.38	13.831%	$85.8058	$85.81	$85.80	$85.80
Purchase #7	$158.86	11.302%	$176.8144	$176.81	$176.80	$176.80
7 purchase totals =	$647.73		$706.0382	$706.04	$706.00	$706.00