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	$80.51	3.724%	$83.5082	$83.51	$83.50	$83.50
Purchase #2	$74.82	5.238%	$78.7391	$78.74	$78.75	$78.70
Purchase #3	$185.79	6.453%	$197.779	$197.78	$197.80	$197.80
Purchase #4	$67.46	3.725%	$69.9729	$69.97	$69.95	$70.00
Purchase #5	$189.62	3.688%	$196.6132	$196.61	$196.60	$196.60
Purchase #6	$42.45	12.391%	$47.71	$47.71	$47.70	$47.70
Purchase #7	$58.41	8.641%	$63.4572	$63.46	$63.45	$63.50
7 purchase totals =	$699.06		$737.7796	$737.78	$737.75	$737.80