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	$103.54	11.270%	$115.209	$115.21	$115.20	$115.20
Purchase #2	$236.52	9.636%	$259.3111	$259.31	$259.30	$259.30
Purchase #3	$100.88	10.715%	$111.6893	$111.69	$111.70	$111.70
Purchase #4	$65.92	8.665%	$71.632	$71.63	$71.65	$71.60
Purchase #5	$33.98	13.580%	$38.5945	$38.59	$38.60	$38.60
Purchase #6	$35.80	11.857%	$40.0448	$40.04	$40.05	$40.00
Purchase #7	$169.41	10.311%	$186.8779	$186.88	$186.90	$186.90
7 purchase totals =	$746.05		$823.3586	$823.35	$823.40	$823.30