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	$72.79	8.128%	$78.7064	$78.71	$78.70	$78.70
Purchase #2	$22.75	5.664%	$24.0386	$24.04	$24.05	$24.00
Purchase #3	$180.75	13.736%	$205.5778	$205.58	$205.60	$205.60
Purchase #4	$106.92	7.354%	$114.7829	$114.78	$114.80	$114.80
Purchase #5	$95.46	6.689%	$101.8453	$101.85	$101.85	$101.80
Purchase #6	$166.58	4.768%	$174.5225	$174.52	$174.50	$174.50
Purchase #7	$197.35	12.696%	$222.4056	$222.41	$222.40	$222.40
7 purchase totals =	$842.60		$921.8791	$921.89	$921.90	$921.80