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	$250.41	12.402%	$281.4658	$281.47	$281.45	$281.50
Purchase #2	$136.38	8.437%	$147.8864	$147.89	$147.90	$147.90
Purchase #3	$169.80	10.115%	$186.9753	$186.98	$187.00	$187.00
Purchase #4	$123.53	4.278%	$128.8146	$128.81	$128.80	$128.80
Purchase #5	$86.96	3.190%	$89.734	$89.73	$89.75	$89.70
Purchase #6	$104.52	13.590%	$118.7243	$118.72	$118.70	$118.70
Purchase #7	$42.68	5.236%	$44.9147	$44.91	$44.90	$44.90
7 purchase totals =	$914.28		$998.5151	$998.51	$998.50	$998.50