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	$142.67	3.758%	$148.0315	$148.03	$148.05	$148.00
Purchase #2	$242.25	7.870%	$261.3151	$261.32	$261.30	$261.30
Purchase #3	$53.45	10.578%	$59.1039	$59.10	$59.10	$59.10
Purchase #4	$160.82	4.633%	$168.2708	$168.27	$168.25	$168.30
Purchase #5	$150.82	10.674%	$166.9185	$166.92	$166.90	$166.90
Purchase #6	$108.52	10.653%	$120.0806	$120.08	$120.10	$120.10
Purchase #7	$30.97	13.373%	$35.1116	$35.11	$35.10	$35.10
7 purchase totals =	$889.50		$958.8320	$958.83	$958.80	$958.80