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	$128.75	8.170%	$139.2689	$139.27	$139.25	$139.30
Purchase #2	$17.97	11.310%	$20.0024	$20.00	$20.00	$20.00
Purchase #3	$146.89	6.500%	$156.4379	$156.44	$156.45	$156.40
Purchase #4	$60.66	10.650%	$67.1203	$67.12	$67.10	$67.10
Purchase #5	$46.66	12.152%	$52.3301	$52.33	$52.35	$52.30
Purchase #6	$19.85	4.742%	$20.7913	$20.79	$20.80	$20.80
Purchase #7	$39.63	6.340%	$42.1425	$42.14	$42.15	$42.10
7 purchase totals =	$460.41		$498.0934	$498.09	$498.10	$498.00