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	$80.98	12.150%	$90.8191	$90.82	$90.80	$90.80
Purchase #2	$63.92	12.629%	$71.9925	$71.99	$72.00	$72.00
Purchase #3	$29.64	9.476%	$32.4487	$32.45	$32.45	$32.40
Purchase #4	$232.47	11.592%	$259.4179	$259.42	$259.40	$259.40
Purchase #5	$202.99	10.862%	$225.0388	$225.04	$225.05	$225.00
Purchase #6	$188.90	10.775%	$209.254	$209.25	$209.25	$209.30
Purchase #7	$111.79	3.734%	$115.9642	$115.96	$115.95	$116.00
7 purchase totals =	$910.69		$1,004.9352	$1,004.93	$1,004.90	$1,004.90