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	$100.88	3.438%	$104.3483	$104.35	$104.35	$104.30
Purchase #2	$142.37	13.675%	$161.8391	$161.84	$161.85	$161.80
Purchase #3	$140.58	7.260%	$150.7861	$150.79	$150.80	$150.80
Purchase #4	$243.30	11.624%	$271.5812	$271.58	$271.60	$271.60
Purchase #5	$20.58	4.581%	$21.5228	$21.52	$21.50	$21.50
Purchase #6	$228.90	3.766%	$237.5204	$237.52	$237.50	$237.50
Purchase #7	$38.72	3.399%	$40.0361	$40.04	$40.05	$40.00
7 purchase totals =	$915.33		$987.6340	$987.64	$987.65	$987.50