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	$43.90	11.366%	$48.8897	$48.89	$48.90	$48.90
Purchase #2	$48.90	4.531%	$51.1157	$51.12	$51.10	$51.10
Purchase #3	$28.30	5.356%	$29.8157	$29.82	$29.80	$29.80
Purchase #4	$97.39	12.869%	$109.9231	$109.92	$109.90	$109.90
Purchase #5	$148.32	11.197%	$164.9274	$164.93	$164.95	$164.90
Purchase #6	$233.52	11.775%	$261.017	$261.02	$261.00	$261.00
Purchase #7	$171.95	11.848%	$192.3226	$192.32	$192.30	$192.30
7 purchase totals =	$772.28		$858.0112	$858.02	$857.95	$857.90