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	$38.55	12.593%	$43.4046	$43.40	$43.40	$43.40
Purchase #2	$141.92	13.293%	$160.7854	$160.79	$160.80	$160.80
Purchase #3	$146.78	9.235%	$160.3351	$160.34	$160.35	$160.30
Purchase #4	$162.36	11.711%	$181.374	$181.37	$181.35	$181.40
Purchase #5	$125.94	11.152%	$139.9848	$139.98	$140.00	$140.00
Purchase #6	$77.52	7.802%	$83.5681	$83.57	$83.55	$83.60
Purchase #7	$142.32	6.463%	$151.5181	$151.52	$151.50	$151.50
7 purchase totals =	$835.39		$920.9701	$920.97	$920.95	$921.00