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	$81.28	10.171%	$89.547	$89.55	$89.55	$89.50
Purchase #2	$250.29	5.808%	$264.8268	$264.83	$264.85	$264.80
Purchase #3	$74.81	6.444%	$79.6308	$79.63	$79.65	$79.60
Purchase #4	$63.46	13.520%	$72.0398	$72.04	$72.05	$72.00
Purchase #5	$174.52	13.706%	$198.4397	$198.44	$198.45	$198.40
Purchase #6	$126.71	7.642%	$136.3932	$136.39	$136.40	$136.40
Purchase #7	$215.78	3.745%	$223.861	$223.86	$223.85	$223.90
7 purchase totals =	$986.85		$1,064.7383	$1,064.74	$1,064.80	$1,064.60