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	$35.69	11.776%	$39.8929	$39.89	$39.90	$39.90
Purchase #2	$211.61	6.517%	$225.4006	$225.40	$225.40	$225.40
Purchase #3	$146.54	12.523%	$164.8912	$164.89	$164.90	$164.90
Purchase #4	$56.89	12.868%	$64.2106	$64.21	$64.20	$64.20
Purchase #5	$147.43	3.441%	$152.5031	$152.50	$152.50	$152.50
Purchase #6	$140.30	13.189%	$158.8042	$158.80	$158.80	$158.80
Purchase #7	$147.58	13.445%	$167.4221	$167.42	$167.40	$167.40
7 purchase totals =	$886.04		$973.1247	$973.11	$973.10	$973.10