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	$41.72	6.656%	$44.4969	$44.50	$44.50	$44.50
Purchase #2	$211.54	4.166%	$220.3528	$220.35	$220.35	$220.40
Purchase #3	$166.75	9.383%	$182.3962	$182.40	$182.40	$182.40
Purchase #4	$41.57	4.457%	$43.4228	$43.42	$43.40	$43.40
Purchase #5	$246.64	3.382%	$254.9814	$254.98	$255.00	$255.00
Purchase #6	$189.85	5.574%	$200.4322	$200.43	$200.45	$200.40
Purchase #7	$111.84	12.459%	$125.7741	$125.77	$125.75	$125.80
7 purchase totals =	$1,009.91		$1,071.8564	$1,071.85	$1,071.85	$1,071.90