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	$53.59	4.332%	$55.9115	$55.91	$55.90	$55.90
Purchase #2	$77.34	5.518%	$81.6076	$81.61	$81.60	$81.60
Purchase #3	$45.33	4.521%	$47.3794	$47.38	$47.40	$47.40
Purchase #4	$100.66	8.757%	$109.4748	$109.47	$109.45	$109.50
Purchase #5	$80.71	10.553%	$89.2273	$89.23	$89.25	$89.20
Purchase #6	$17.37	10.347%	$19.1673	$19.17	$19.15	$19.20
Purchase #7	$236.43	11.165%	$262.8274	$262.83	$262.85	$262.80
7 purchase totals =	$611.43		$665.5953	$665.60	$665.60	$665.60