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	$74.86	6.674%	$79.8562	$79.86	$79.85	$79.90
Purchase #2	$106.84	4.437%	$111.5805	$111.58	$111.60	$111.60
Purchase #3	$79.42	12.814%	$89.5969	$89.60	$89.60	$89.60
Purchase #4	$33.60	4.871%	$35.2367	$35.24	$35.25	$35.20
Purchase #5	$59.56	13.261%	$67.4583	$67.46	$67.45	$67.50
Purchase #6	$98.38	10.210%	$108.4246	$108.42	$108.40	$108.40
Purchase #7	$31.52	13.550%	$35.791	$35.79	$35.80	$35.80
7 purchase totals =	$484.18		$527.9442	$527.95	$527.95	$528.00