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	$35.72	10.586%	$39.5013	$39.50	$39.50	$39.50
Purchase #2	$17.85	3.290%	$18.4373	$18.44	$18.45	$18.40
Purchase #3	$128.31	6.855%	$137.1057	$137.11	$137.10	$137.10
Purchase #4	$142.60	9.575%	$156.254	$156.25	$156.25	$156.30
Purchase #5	$178.96	7.127%	$191.7145	$191.71	$191.70	$191.70
Purchase #6	$79.73	8.611%	$86.5956	$86.60	$86.60	$86.60
Purchase #7	$85.40	8.704%	$92.8332	$92.83	$92.85	$92.80
7 purchase totals =	$668.57		$722.4416	$722.44	$722.45	$722.40