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	$153.25	6.704%	$163.5239	$163.52	$163.50	$163.50
Purchase #2	$91.83	13.543%	$104.2665	$104.27	$104.25	$104.30
Purchase #3	$173.40	13.517%	$196.8385	$196.84	$196.85	$196.80
Purchase #4	$239.72	8.583%	$260.2952	$260.30	$260.30	$260.30
Purchase #5	$191.93	6.550%	$204.5014	$204.50	$204.50	$204.50
Purchase #6	$84.94	4.658%	$88.8965	$88.90	$88.90	$88.90
Purchase #7	$119.70	7.447%	$128.6141	$128.61	$128.60	$128.60
7 purchase totals =	$1,054.77		$1,146.9361	$1,146.94	$1,146.90	$1,146.90