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	$19.59	3.357%	$20.2476	$20.25	$20.25	$20.20
Purchase #2	$184.33	6.803%	$196.87	$196.87	$196.85	$196.90
Purchase #3	$57.81	8.707%	$62.8435	$62.84	$62.85	$62.80
Purchase #4	$105.45	9.443%	$115.4076	$115.41	$115.40	$115.40
Purchase #5	$42.92	4.314%	$44.7716	$44.77	$44.75	$44.80
Purchase #6	$86.33	12.111%	$96.7854	$96.79	$96.80	$96.80
Purchase #7	$192.35	4.266%	$200.5557	$200.56	$200.55	$200.60
7 purchase totals =	$688.78		$737.4814	$737.49	$737.45	$737.50