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	$19.36	5.734%	$20.4701	$20.47	$20.45	$20.50
Purchase #2	$59.85	3.185%	$61.7562	$61.76	$61.75	$61.80
Purchase #3	$76.70	12.606%	$86.3688	$86.37	$86.35	$86.40
Purchase #4	$66.97	9.858%	$73.5719	$73.57	$73.55	$73.60
Purchase #5	$240.52	11.632%	$268.4973	$268.50	$268.50	$268.50
Purchase #6	$236.73	7.811%	$255.221	$255.22	$255.20	$255.20
Purchase #7	$133.64	8.416%	$144.8871	$144.89	$144.90	$144.90
7 purchase totals =	$833.77		$910.7724	$910.78	$910.70	$910.90