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	$166.38	8.193%	$180.0115	$180.01	$180.00	$180.00
Purchase #2	$162.72	3.618%	$168.6072	$168.61	$168.60	$168.60
Purchase #3	$23.45	3.155%	$24.1898	$24.19	$24.20	$24.20
Purchase #4	$134.56	5.385%	$141.8061	$141.81	$141.80	$141.80
Purchase #5	$203.26	3.712%	$210.805	$210.81	$210.80	$210.80
Purchase #6	$188.92	11.172%	$210.0261	$210.03	$210.05	$210.00
Purchase #7	$79.35	12.805%	$89.5108	$89.51	$89.50	$89.50
7 purchase totals =	$958.64		$1,024.9565	$1,024.97	$1,024.95	$1,024.90