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	$123.86	9.126%	$135.1635	$135.16	$135.15	$135.20
Purchase #2	$99.89	5.445%	$105.329	$105.33	$105.35	$105.30
Purchase #3	$161.45	11.696%	$180.3332	$180.33	$180.35	$180.30
Purchase #4	$106.38	13.679%	$120.9317	$120.93	$120.95	$120.90
Purchase #5	$38.42	9.721%	$42.1548	$42.15	$42.15	$42.20
Purchase #6	$87.57	13.116%	$99.0557	$99.06	$99.05	$99.10
Purchase #7	$135.76	3.378%	$140.346	$140.35	$140.35	$140.30
7 purchase totals =	$753.33		$823.3139	$823.31	$823.35	$823.30