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	$199.47	11.653%	$222.7142	$222.71	$222.70	$222.70
Purchase #2	$94.83	8.819%	$103.1931	$103.19	$103.20	$103.20
Purchase #3	$30.57	9.616%	$33.5096	$33.51	$33.50	$33.50
Purchase #4	$191.55	7.859%	$206.6039	$206.60	$206.60	$206.60
Purchase #5	$108.76	3.803%	$112.8961	$112.90	$112.90	$112.90
Purchase #6	$211.78	3.406%	$218.9932	$218.99	$219.00	$219.00
Purchase #7	$99.67	6.298%	$105.9472	$105.95	$105.95	$105.90
7 purchase totals =	$936.63		$1,003.8573	$1,003.85	$1,003.85	$1,003.80