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	$95.83	7.857%	$103.3594	$103.36	$103.35	$103.40
Purchase #2	$132.82	5.109%	$139.6058	$139.61	$139.60	$139.60
Purchase #3	$124.31	6.192%	$132.0073	$132.01	$132.00	$132.00
Purchase #4	$24.75	6.203%	$26.2852	$26.29	$26.30	$26.30
Purchase #5	$178.53	7.221%	$191.4217	$191.42	$191.40	$191.40
Purchase #6	$47.55	10.377%	$52.4843	$52.48	$52.50	$52.50
Purchase #7	$181.77	4.695%	$190.3041	$190.30	$190.30	$190.30
7 purchase totals =	$785.56		$835.4678	$835.47	$835.45	$835.50