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	$80.60	11.631%	$89.9746	$89.97	$89.95	$90.00
Purchase #2	$87.78	12.336%	$98.6085	$98.61	$98.60	$98.60
Purchase #3	$80.37	5.723%	$84.9696	$84.97	$84.95	$85.00
Purchase #4	$125.62	10.797%	$139.1832	$139.18	$139.20	$139.20
Purchase #5	$216.25	4.319%	$225.5898	$225.59	$225.60	$225.60
Purchase #6	$53.30	12.180%	$59.7919	$59.79	$59.80	$59.80
Purchase #7	$21.86	8.524%	$23.7233	$23.72	$23.70	$23.70
7 purchase totals =	$665.78		$721.8409	$721.83	$721.80	$721.90