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	$115.50	4.565%	$120.7726	$120.77	$120.75	$120.80
Purchase #2	$37.99	10.571%	$42.0059	$42.01	$42.00	$42.00
Purchase #3	$72.39	7.502%	$77.8207	$77.82	$77.80	$77.80
Purchase #4	$120.44	3.666%	$124.8553	$124.86	$124.85	$124.90
Purchase #5	$158.55	8.841%	$172.5674	$172.57	$172.55	$172.60
Purchase #6	$6.67	11.134%	$7.4126	$7.41	$7.40	$7.40
Purchase #7	$215.89	4.617%	$225.8576	$225.86	$225.85	$225.90
7 purchase totals =	$727.43		$771.2921	$771.30	$771.20	$771.40