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	$87.97	4.250%	$91.7087	$91.71	$91.70	$91.70
Purchase #2	$175.40	8.268%	$189.9021	$189.90	$189.90	$189.90
Purchase #3	$123.71	6.313%	$131.5198	$131.52	$131.50	$131.50
Purchase #4	$185.92	4.606%	$194.4835	$194.48	$194.50	$194.50
Purchase #5	$90.94	13.585%	$103.2942	$103.29	$103.30	$103.30
Purchase #6	$7.85	3.423%	$8.1187	$8.12	$8.10	$8.10
Purchase #7	$166.29	9.748%	$182.4999	$182.50	$182.50	$182.50
7 purchase totals =	$838.08		$901.5269	$901.52	$901.50	$901.50