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	$122.40	11.589%	$136.5849	$136.58	$136.60	$136.60
Purchase #2	$99.33	12.262%	$111.5098	$111.51	$111.50	$111.50
Purchase #3	$42.77	11.860%	$47.8425	$47.84	$47.85	$47.80
Purchase #4	$213.63	9.314%	$233.5275	$233.53	$233.55	$233.50
Purchase #5	$119.62	3.402%	$123.6895	$123.69	$123.70	$123.70
Purchase #6	$59.99	5.532%	$63.3086	$63.31	$63.30	$63.30
Purchase #7	$64.90	10.178%	$71.5055	$71.51	$71.50	$71.50
7 purchase totals =	$722.64		$787.9683	$787.97	$788.00	$787.90