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	$38.77	5.295%	$40.8229	$40.82	$40.80	$40.80
Purchase #2	$226.96	12.261%	$254.7876	$254.79	$254.80	$254.80
Purchase #3	$109.58	12.791%	$123.5964	$123.60	$123.60	$123.60
Purchase #4	$42.39	3.656%	$43.9398	$43.94	$43.95	$43.90
Purchase #5	$186.61	8.421%	$202.3244	$202.32	$202.30	$202.30
Purchase #6	$113.28	13.391%	$128.4493	$128.45	$128.45	$128.40
Purchase #7	$231.72	11.638%	$258.6876	$258.69	$258.70	$258.70
7 purchase totals =	$949.31		$1,052.6080	$1,052.61	$1,052.60	$1,052.50