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	$125.53	8.811%	$136.5904	$136.59	$136.60	$136.60
Purchase #2	$117.53	9.678%	$128.9046	$128.90	$128.90	$128.90
Purchase #3	$184.71	6.524%	$196.7605	$196.76	$196.75	$196.80
Purchase #4	$117.32	8.167%	$126.9015	$126.90	$126.90	$126.90
Purchase #5	$179.73	4.803%	$188.3624	$188.36	$188.35	$188.40
Purchase #6	$231.67	4.277%	$241.5785	$241.58	$241.60	$241.60
Purchase #7	$242.32	3.293%	$250.2996	$250.30	$250.30	$250.30
7 purchase totals =	$1,198.81		$1,269.3975	$1,269.39	$1,269.40	$1,269.50