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	$39.29	4.360%	$41.003	$41.00	$41.00	$41.00
Purchase #2	$250.53	10.538%	$276.9309	$276.93	$276.95	$276.90
Purchase #3	$104.31	11.686%	$116.4997	$116.50	$116.50	$116.50
Purchase #4	$20.82	8.196%	$22.5264	$22.53	$22.55	$22.50
Purchase #5	$193.97	9.530%	$212.4553	$212.46	$212.45	$212.50
Purchase #6	$113.92	12.650%	$128.3309	$128.33	$128.35	$128.30
Purchase #7	$125.83	4.372%	$131.3313	$131.33	$131.35	$131.30
7 purchase totals =	$848.67		$929.0775	$929.08	$929.15	$929.00