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	$38.68	5.763%	$40.9091	$40.91	$40.90	$40.90
Purchase #2	$161.43	5.855%	$170.8817	$170.88	$170.90	$170.90
Purchase #3	$27.99	13.794%	$31.8509	$31.85	$31.85	$31.90
Purchase #4	$129.33	5.465%	$136.3979	$136.40	$136.40	$136.40
Purchase #5	$224.30	9.465%	$245.53	$245.53	$245.55	$245.50
Purchase #6	$95.98	10.308%	$105.8736	$105.87	$105.85	$105.90
Purchase #7	$62.85	12.736%	$70.8546	$70.85	$70.85	$70.90
7 purchase totals =	$740.56		$802.2978	$802.29	$802.30	$802.40