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	$38.76	9.639%	$42.4961	$42.50	$42.50	$42.50
Purchase #2	$134.66	12.488%	$151.4763	$151.48	$151.50	$151.50
Purchase #3	$250.72	5.331%	$264.0859	$264.09	$264.10	$264.10
Purchase #4	$62.83	7.316%	$67.4266	$67.43	$67.45	$67.40
Purchase #5	$102.41	3.594%	$106.0906	$106.09	$106.10	$106.10
Purchase #6	$107.44	4.473%	$112.2458	$112.25	$112.25	$112.20
Purchase #7	$201.30	12.726%	$226.9174	$226.92	$226.90	$226.90
7 purchase totals =	$898.12		$970.7387	$970.76	$970.80	$970.70