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	$135.33	12.175%	$151.8064	$151.81	$151.80	$151.80
Purchase #2	$81.40	4.598%	$85.1428	$85.14	$85.15	$85.10
Purchase #3	$64.54	5.440%	$68.051	$68.05	$68.05	$68.10
Purchase #4	$199.35	11.130%	$221.5377	$221.54	$221.55	$221.50
Purchase #5	$231.60	11.638%	$258.5536	$258.55	$258.55	$258.60
Purchase #6	$80.26	10.338%	$88.5573	$88.56	$88.55	$88.60
Purchase #7	$39.38	3.574%	$40.7874	$40.79	$40.80	$40.80
7 purchase totals =	$831.86		$914.4362	$914.44	$914.45	$914.50