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	$33.39	10.302%	$36.8298	$36.83	$36.85	$36.80
Purchase #2	$102.82	6.537%	$109.5413	$109.54	$109.55	$109.50
Purchase #3	$185.40	13.146%	$209.7727	$209.77	$209.75	$209.80
Purchase #4	$118.72	10.829%	$131.5762	$131.58	$131.60	$131.60
Purchase #5	$56.41	13.132%	$63.8178	$63.82	$63.80	$63.80
Purchase #6	$113.70	11.274%	$126.5185	$126.52	$126.50	$126.50
Purchase #7	$168.67	6.723%	$180.0097	$180.01	$180.00	$180.00
7 purchase totals =	$779.11		$858.0660	$858.07	$858.05	$858.00