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	$240.72	11.298%	$267.9165	$267.92	$267.90	$267.90
Purchase #2	$213.78	7.364%	$229.5228	$229.52	$229.50	$229.50
Purchase #3	$108.87	6.462%	$115.9052	$115.91	$115.90	$115.90
Purchase #4	$169.39	6.544%	$180.4749	$180.47	$180.45	$180.50
Purchase #5	$93.97	6.231%	$99.8253	$99.83	$99.85	$99.80
Purchase #6	$100.80	10.564%	$111.4485	$111.45	$111.45	$111.40
Purchase #7	$104.26	7.725%	$112.3141	$112.31	$112.30	$112.30
7 purchase totals =	$1,031.79		$1,117.4073	$1,117.41	$1,117.35	$1,117.30