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	$123.89	11.363%	$137.9676	$137.97	$137.95	$138.00
Purchase #2	$35.84	11.543%	$39.977	$39.98	$40.00	$40.00
Purchase #3	$168.61	10.579%	$186.4473	$186.45	$186.45	$186.40
Purchase #4	$169.85	9.673%	$186.2796	$186.28	$186.30	$186.30
Purchase #5	$245.65	8.240%	$265.8916	$265.89	$265.90	$265.90
Purchase #6	$91.87	11.700%	$102.6188	$102.62	$102.60	$102.60
Purchase #7	$238.54	9.715%	$261.7142	$261.71	$261.70	$261.70
7 purchase totals =	$1,074.25		$1,180.8961	$1,180.90	$1,180.90	$1,180.90