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	$108.71	6.465%	$115.7381	$115.74	$115.75	$115.70
Purchase #2	$155.58	9.610%	$170.5312	$170.53	$170.55	$170.50
Purchase #3	$225.53	3.728%	$233.9378	$233.94	$233.95	$233.90
Purchase #4	$218.45	11.630%	$243.8557	$243.86	$243.85	$243.90
Purchase #5	$158.76	12.123%	$178.0065	$178.01	$178.00	$178.00
Purchase #6	$41.33	4.261%	$43.0911	$43.09	$43.10	$43.10
Purchase #7	$52.67	12.709%	$59.3638	$59.36	$59.35	$59.40
7 purchase totals =	$961.03		$1,044.5242	$1,044.53	$1,044.55	$1,044.50