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	$232.82	10.385%	$256.9984	$257.00	$257.00	$257.00
Purchase #2	$51.45	6.531%	$54.8102	$54.81	$54.80	$54.80
Purchase #3	$54.25	10.132%	$59.7466	$59.75	$59.75	$59.70
Purchase #4	$120.38	7.668%	$129.6107	$129.61	$129.60	$129.60
Purchase #5	$123.83	4.121%	$128.933	$128.93	$128.95	$128.90
Purchase #6	$142.93	6.562%	$152.3091	$152.31	$152.30	$152.30
Purchase #7	$194.70	3.480%	$201.4756	$201.48	$201.50	$201.50
7 purchase totals =	$920.36		$983.8836	$983.89	$983.90	$983.80