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	$35.81	13.381%	$40.6017	$40.60	$40.60	$40.60
Purchase #2	$125.58	4.767%	$131.5664	$131.57	$131.55	$131.60
Purchase #3	$79.47	13.447%	$90.1563	$90.16	$90.15	$90.20
Purchase #4	$146.91	4.621%	$153.6987	$153.70	$153.70	$153.70
Purchase #5	$188.70	8.684%	$205.0867	$205.09	$205.10	$205.10
Purchase #6	$80.87	7.374%	$86.8334	$86.83	$86.85	$86.80
Purchase #7	$138.32	8.513%	$150.0952	$150.10	$150.10	$150.10
7 purchase totals =	$795.66		$858.0384	$858.05	$858.05	$858.10