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	$159.69	4.266%	$166.5024	$166.50	$166.50	$166.50
Purchase #2	$16.46	10.859%	$18.2474	$18.25	$18.25	$18.20
Purchase #3	$202.60	6.298%	$215.3597	$215.36	$215.35	$215.40
Purchase #4	$113.65	4.566%	$118.8393	$118.84	$118.85	$118.80
Purchase #5	$128.71	6.256%	$136.7621	$136.76	$136.75	$136.80
Purchase #6	$100.45	11.761%	$112.2639	$112.26	$112.25	$112.30
Purchase #7	$104.30	8.271%	$112.9267	$112.93	$112.95	$112.90
7 purchase totals =	$825.86		$880.9015	$880.90	$880.90	$880.90