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	$44.79	13.604%	$50.8832	$50.88	$50.90	$50.90
Purchase #2	$177.68	11.809%	$198.6622	$198.66	$198.65	$198.70
Purchase #3	$137.82	10.847%	$152.7693	$152.77	$152.75	$152.80
Purchase #4	$166.38	13.699%	$189.1724	$189.17	$189.15	$189.20
Purchase #5	$237.86	12.672%	$268.0016	$268.00	$268.00	$268.00
Purchase #6	$30.27	4.381%	$31.5961	$31.60	$31.60	$31.60
Purchase #7	$56.86	4.230%	$59.2652	$59.27	$59.25	$59.30
7 purchase totals =	$851.66		$950.3500	$950.35	$950.30	$950.50