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	$7.85	12.442%	$8.8267	$8.83	$8.85	$8.80
Purchase #2	$128.76	10.484%	$142.2592	$142.26	$142.25	$142.30
Purchase #3	$6.87	4.191%	$7.1579	$7.16	$7.15	$7.20
Purchase #4	$13.51	10.448%	$14.9215	$14.92	$14.90	$14.90
Purchase #5	$218.44	4.128%	$227.4572	$227.46	$227.45	$227.50
Purchase #6	$35.35	7.145%	$37.8758	$37.88	$37.90	$37.90
Purchase #7	$55.88	6.822%	$59.6921	$59.69	$59.70	$59.70
7 purchase totals =	$466.66		$498.1904	$498.20	$498.20	$498.30