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	$84.70	5.237%	$89.1357	$89.14	$89.15	$89.10
Purchase #2	$181.33	5.868%	$191.9704	$191.97	$191.95	$192.00
Purchase #3	$169.45	4.172%	$176.5195	$176.52	$176.50	$176.50
Purchase #4	$245.57	6.132%	$260.6284	$260.63	$260.65	$260.60
Purchase #5	$91.74	8.594%	$99.6241	$99.62	$99.60	$99.60
Purchase #6	$170.89	10.630%	$189.0556	$189.06	$189.05	$189.10
Purchase #7	$137.28	10.778%	$152.076	$152.08	$152.10	$152.10
7 purchase totals =	$1,080.96		$1,159.0097	$1,159.02	$1,159.00	$1,159.00