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	$152.49	10.629%	$168.6982	$168.70	$168.70	$168.70
Purchase #2	$78.43	3.799%	$81.4096	$81.41	$81.40	$81.40
Purchase #3	$61.36	13.299%	$69.5203	$69.52	$69.50	$69.50
Purchase #4	$214.27	6.161%	$227.4712	$227.47	$227.45	$227.50
Purchase #5	$17.66	5.421%	$18.6173	$18.62	$18.60	$18.60
Purchase #6	$127.79	10.850%	$141.6552	$141.66	$141.65	$141.70
Purchase #7	$132.40	7.423%	$142.2281	$142.23	$142.25	$142.20
7 purchase totals =	$784.40		$849.5999	$849.61	$849.55	$849.60