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	$90.45	9.439%	$98.9876	$98.99	$99.00	$99.00
Purchase #2	$54.57	10.679%	$60.3975	$60.40	$60.40	$60.40
Purchase #3	$178.35	10.201%	$196.5435	$196.54	$196.55	$196.50
Purchase #4	$104.67	10.170%	$115.3149	$115.31	$115.30	$115.30
Purchase #5	$63.32	6.315%	$67.3187	$67.32	$67.30	$67.30
Purchase #6	$176.32	13.545%	$200.2025	$200.20	$200.20	$200.20
Purchase #7	$21.86	12.208%	$24.5287	$24.53	$24.55	$24.50
7 purchase totals =	$689.54		$763.2934	$763.29	$763.30	$763.20