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	$222.70	11.611%	$248.5577	$248.56	$248.55	$248.60
Purchase #2	$57.40	3.798%	$59.5801	$59.58	$59.60	$59.60
Purchase #3	$98.64	12.140%	$110.6149	$110.61	$110.60	$110.60
Purchase #4	$142.47	8.217%	$154.1768	$154.18	$154.20	$154.20
Purchase #5	$11.66	10.852%	$12.9253	$12.93	$12.95	$12.90
Purchase #6	$180.70	5.619%	$190.8535	$190.85	$190.85	$190.90
Purchase #7	$140.27	6.106%	$148.8349	$148.83	$148.85	$148.80
7 purchase totals =	$853.84		$925.5432	$925.54	$925.60	$925.60