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	$243.72	6.305%	$259.0865	$259.09	$259.10	$259.10
Purchase #2	$185.66	9.618%	$203.5168	$203.52	$203.50	$203.50
Purchase #3	$139.99	10.819%	$155.1355	$155.14	$155.15	$155.10
Purchase #4	$205.65	6.190%	$218.3797	$218.38	$218.40	$218.40
Purchase #5	$94.96	8.314%	$102.855	$102.86	$102.85	$102.90
Purchase #6	$40.30	11.181%	$44.8059	$44.81	$44.80	$44.80
Purchase #7	$105.55	3.824%	$109.5862	$109.59	$109.60	$109.60
7 purchase totals =	$1,015.83		$1,093.3656	$1,093.39	$1,093.40	$1,093.40