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	$250.60	5.187%	$263.5986	$263.60	$263.60	$263.60
Purchase #2	$223.35	12.164%	$250.5183	$250.52	$250.50	$250.50
Purchase #3	$229.34	11.783%	$256.3631	$256.36	$256.35	$256.40
Purchase #4	$183.46	13.791%	$208.761	$208.76	$208.75	$208.80
Purchase #5	$237.58	12.293%	$266.7857	$266.79	$266.80	$266.80
Purchase #6	$136.32	10.661%	$150.8531	$150.85	$150.85	$150.90
Purchase #7	$181.90	3.108%	$187.5535	$187.55	$187.55	$187.60
7 purchase totals =	$1,442.55		$1,584.4333	$1,584.43	$1,584.40	$1,584.60