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	$166.91	11.125%	$185.4787	$185.48	$185.50	$185.50
Purchase #2	$123.91	6.360%	$131.7907	$131.79	$131.80	$131.80
Purchase #3	$150.53	10.802%	$166.7903	$166.79	$166.80	$166.80
Purchase #4	$33.56	7.714%	$36.1488	$36.15	$36.15	$36.10
Purchase #5	$110.67	9.699%	$121.4039	$121.40	$121.40	$121.40
Purchase #6	$78.43	5.723%	$82.9185	$82.92	$82.90	$82.90
Purchase #7	$162.44	12.709%	$183.0845	$183.08	$183.10	$183.10
7 purchase totals =	$826.45		$907.6154	$907.61	$907.65	$907.60