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	$134.41	5.328%	$141.5714	$141.57	$141.55	$141.60
Purchase #2	$99.99	9.530%	$109.519	$109.52	$109.50	$109.50
Purchase #3	$242.73	4.558%	$253.7936	$253.79	$253.80	$253.80
Purchase #4	$104.86	6.728%	$111.915	$111.92	$111.90	$111.90
Purchase #5	$43.71	12.278%	$49.0767	$49.08	$49.10	$49.10
Purchase #6	$182.60	3.665%	$189.2923	$189.29	$189.30	$189.30
Purchase #7	$133.99	6.233%	$142.3416	$142.34	$142.35	$142.30
7 purchase totals =	$942.29		$997.5096	$997.51	$997.50	$997.50