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	$136.45	4.321%	$142.346	$142.35	$142.35	$142.30
Purchase #2	$208.56	13.217%	$236.1254	$236.13	$236.15	$236.10
Purchase #3	$170.40	5.355%	$179.5249	$179.52	$179.50	$179.50
Purchase #4	$222.55	12.341%	$250.0149	$250.01	$250.00	$250.00
Purchase #5	$45.27	5.542%	$47.7789	$47.78	$47.80	$47.80
Purchase #6	$18.87	9.463%	$20.6557	$20.66	$20.65	$20.70
Purchase #7	$45.47	13.398%	$51.5621	$51.56	$51.55	$51.60
7 purchase totals =	$847.57		$928.0079	$928.01	$928.00	$928.00