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	$200.75	13.716%	$228.2849	$228.28	$228.30	$228.30
Purchase #2	$151.38	11.206%	$168.3436	$168.34	$168.35	$168.30
Purchase #3	$29.90	10.235%	$32.9603	$32.96	$32.95	$33.00
Purchase #4	$19.60	11.600%	$21.8736	$21.87	$21.85	$21.90
Purchase #5	$213.63	12.762%	$240.8935	$240.89	$240.90	$240.90
Purchase #6	$92.86	11.281%	$103.3355	$103.34	$103.35	$103.30
Purchase #7	$168.98	3.214%	$174.411	$174.41	$174.40	$174.40
7 purchase totals =	$877.10		$970.1024	$970.09	$970.10	$970.10