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	$213.53	6.718%	$227.8749	$227.87	$227.85	$227.90
Purchase #2	$82.90	5.590%	$87.5341	$87.53	$87.55	$87.50
Purchase #3	$234.39	12.786%	$264.3591	$264.36	$264.35	$264.40
Purchase #4	$69.58	9.505%	$76.1936	$76.19	$76.20	$76.20
Purchase #5	$84.28	6.339%	$89.6225	$89.62	$89.60	$89.60
Purchase #6	$81.75	9.854%	$89.8056	$89.81	$89.80	$89.80
Purchase #7	$22.90	9.175%	$25.0011	$25.00	$25.00	$25.00
7 purchase totals =	$789.33		$860.3909	$860.38	$860.35	$860.40