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	$168.33	7.281%	$180.5861	$180.59	$180.60	$180.60
Purchase #2	$116.48	10.237%	$128.4041	$128.40	$128.40	$128.40
Purchase #3	$234.40	9.437%	$256.5203	$256.52	$256.50	$256.50
Purchase #4	$95.63	5.420%	$100.8131	$100.81	$100.80	$100.80
Purchase #5	$219.83	9.142%	$239.9269	$239.93	$239.95	$239.90
Purchase #6	$34.97	13.154%	$39.57	$39.57	$39.55	$39.60
Purchase #7	$72.93	12.751%	$82.2293	$82.23	$82.25	$82.20
7 purchase totals =	$942.57		$1,028.0498	$1,028.05	$1,028.05	$1,028.00