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	$35.45	10.258%	$39.0865	$39.09	$39.10	$39.10
Purchase #2	$139.30	13.404%	$157.9718	$157.97	$157.95	$158.00
Purchase #3	$5.39	11.298%	$5.999	$6.00	$6.00	$6.00
Purchase #4	$195.82	6.375%	$208.3035	$208.30	$208.30	$208.30
Purchase #5	$55.77	3.287%	$57.6032	$57.60	$57.60	$57.60
Purchase #6	$67.73	13.782%	$77.0645	$77.06	$77.05	$77.10
Purchase #7	$74.72	9.799%	$82.0418	$82.04	$82.05	$82.00
7 purchase totals =	$574.18		$628.0703	$628.06	$628.05	$628.10