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	$94.97	8.371%	$102.9199	$102.92	$102.90	$102.90
Purchase #2	$171.82	13.221%	$194.5363	$194.54	$194.55	$194.50
Purchase #3	$140.90	12.396%	$158.366	$158.37	$158.35	$158.40
Purchase #4	$27.90	13.177%	$31.5764	$31.58	$31.60	$31.60
Purchase #5	$153.88	9.681%	$168.7771	$168.78	$168.80	$168.80
Purchase #6	$71.40	12.770%	$80.5178	$80.52	$80.50	$80.50
Purchase #7	$223.72	4.847%	$234.5637	$234.56	$234.55	$234.60
7 purchase totals =	$884.59		$971.2572	$971.27	$971.25	$971.30