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	$220.80	3.261%	$228.0003	$228.00	$228.00	$228.00
Purchase #2	$82.64	13.839%	$94.0765	$94.08	$94.10	$94.10
Purchase #3	$45.80	13.207%	$51.8488	$51.85	$51.85	$51.80
Purchase #4	$83.42	7.781%	$89.9109	$89.91	$89.90	$89.90
Purchase #5	$223.93	7.368%	$240.4292	$240.43	$240.45	$240.40
Purchase #6	$98.69	6.595%	$105.1986	$105.20	$105.20	$105.20
Purchase #7	$139.92	6.153%	$148.5293	$148.53	$148.55	$148.50
7 purchase totals =	$895.20		$957.9936	$958.00	$958.05	$957.90