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	$229.35	4.663%	$240.0446	$240.04	$240.05	$240.00
Purchase #2	$86.46	3.587%	$89.5613	$89.56	$89.55	$89.60
Purchase #3	$48.80	5.734%	$51.5982	$51.60	$51.60	$51.60
Purchase #4	$190.99	9.490%	$209.115	$209.12	$209.10	$209.10
Purchase #5	$83.32	8.355%	$90.2814	$90.28	$90.30	$90.30
Purchase #6	$110.98	3.456%	$114.8155	$114.82	$114.80	$114.80
Purchase #7	$229.65	13.366%	$260.345	$260.35	$260.35	$260.30
7 purchase totals =	$979.55		$1,055.7610	$1,055.77	$1,055.75	$1,055.70