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	$26.50	4.768%	$27.7635	$27.76	$27.75	$27.80
Purchase #2	$192.72	11.490%	$214.8635	$214.86	$214.85	$214.90
Purchase #3	$136.28	4.436%	$142.3254	$142.33	$142.35	$142.30
Purchase #4	$99.77	3.428%	$103.1901	$103.19	$103.20	$103.20
Purchase #5	$125.92	12.802%	$142.0403	$142.04	$142.05	$142.00
Purchase #6	$92.51	11.606%	$103.2467	$103.25	$103.25	$103.20
Purchase #7	$178.88	11.189%	$198.8949	$198.89	$198.90	$198.90
7 purchase totals =	$852.58		$932.3244	$932.32	$932.35	$932.30