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	$21.97	11.366%	$24.4671	$24.47	$24.45	$24.50
Purchase #2	$62.50	11.766%	$69.8538	$69.85	$69.85	$69.90
Purchase #3	$242.25	3.270%	$250.1716	$250.17	$250.15	$250.20
Purchase #4	$245.89	6.386%	$261.5925	$261.59	$261.60	$261.60
Purchase #5	$151.94	9.735%	$166.7314	$166.73	$166.75	$166.70
Purchase #6	$218.40	11.372%	$243.2364	$243.24	$243.25	$243.20
Purchase #7	$167.50	3.234%	$172.917	$172.92	$172.90	$172.90
7 purchase totals =	$1,110.45		$1,188.9698	$1,188.97	$1,188.95	$1,189.00