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	$106.40	11.870%	$119.0297	$119.03	$119.05	$119.00
Purchase #2	$126.93	8.644%	$137.9018	$137.90	$137.90	$137.90
Purchase #3	$45.31	10.646%	$50.1337	$50.13	$50.15	$50.10
Purchase #4	$20.95	4.465%	$21.8854	$21.89	$21.90	$21.90
Purchase #5	$73.75	6.574%	$78.5983	$78.60	$78.60	$78.60
Purchase #6	$68.58	11.265%	$76.3055	$76.31	$76.30	$76.30
Purchase #7	$167.86	9.534%	$183.8638	$183.86	$183.85	$183.90
7 purchase totals =	$609.78		$667.7182	$667.72	$667.75	$667.70