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	$227.50	5.761%	$240.6063	$240.61	$240.60	$240.60
Purchase #2	$245.75	13.596%	$279.1622	$279.16	$279.15	$279.20
Purchase #3	$138.75	13.193%	$157.0553	$157.06	$157.05	$157.10
Purchase #4	$202.36	13.430%	$229.5369	$229.54	$229.55	$229.50
Purchase #5	$66.45	9.153%	$72.5322	$72.53	$72.55	$72.50
Purchase #6	$80.61	11.473%	$89.8584	$89.86	$89.85	$89.90
Purchase #7	$110.38	3.649%	$114.4078	$114.41	$114.40	$114.40
7 purchase totals =	$1,071.80		$1,183.1591	$1,183.17	$1,183.15	$1,183.20