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	$74.80	10.390%	$82.5717	$82.57	$82.55	$82.60
Purchase #2	$41.97	9.759%	$46.0659	$46.07	$46.05	$46.10
Purchase #3	$90.89	10.782%	$100.6898	$100.69	$100.70	$100.70
Purchase #4	$104.35	4.498%	$109.0437	$109.04	$109.05	$109.00
Purchase #5	$9.27	3.794%	$9.6217	$9.62	$9.60	$9.60
Purchase #6	$207.69	8.361%	$225.055	$225.06	$225.05	$225.10
Purchase #7	$84.36	8.414%	$91.4581	$91.46	$91.45	$91.50
7 purchase totals =	$613.33		$664.5059	$664.51	$664.45	$664.60